The Social style of Tango is called Argentine Tango and is in a family with Milonga and Valz. Argentine Tango and Milonga can have a performance quality to it if intended as seen on "Dancing with the Stars", but for the most part is intended for improvising in an intimate setting with the leader creatively interpreting the music on the spot.
What is Argentine Tango?
First of all, Argentine Tango is NOT a "ballroom" dance. Ballroom dances tend to be focused on the audience, performing choreographed patterns, while Argentine Tango is improvised, with every step being a spontaneous, creative discovery, and with the partners focused on each other and on the music. Argentine Tango is almost exclusively a social dance, with each partner focused on enjoying themselves and giving pleasure and enjoyment to their partners. A key feature is that it is not choreographed in a social setting. Every step is led and followed.
There is a lot of disagreement today about some details of the origins of Argentine Tango. However it is generally agreed that it originated in Buenos Aires, Argentina from the late 1800's through the early 1900's. At that time in Argentina there were many thousands of immigrants who had been lured to Argentina with the promise of jobs in the cattle and lumber industries. These immigrants, Italian, Portuguese, Slavic, and Western European, mixed with populations of black slaves, South American indigenous people, Spanish people from the early conquest, and people from other South American and Caribbean countries. And everyone brought with them their cultural history, their music and their dance. The resulting melting pot created what we know today as Argentine Tango.
In the early years, the Tango was only danced in the poor sections of the city, in the Orillero, the "outskirts", and in the dock and industrial areas. The popular legend is that it was the dance in the bordellos in the "red light" districts. This association with the lower classes and the slave populations created a stigma on the dance, and the upper classes of Argentine society shunned and spurned the dance as being vulgar and obscene. This was understandable. Tango then and now is indeed a sensuous and passionate dance, with an intimate embrace and connection between the partners that is unacceptable to more Puritan sensibilities.
But in the 1920's, Tango was "discovered" by wealthy European travelers, and when they took the dance back to Paris, it became the rage of the Roaring 20's. As more Europeans came to Argentina to learn the dance, the economic potential was appreciated, and established Argentine society finally began to accept the dance, and to develop and teach it.
1930's - 1950's
The "Golden Age" of Tango was the period from the 1930's to the 1950's. This was a time of incredible output and evolution of the dance and it's music. The music that was composed in that period, and the orquestas that performed and recorded it, are still the mainstay of Tango dancing. Even today, at Argentina Milongas you will only occasionally hear music that is not from this period.
In the 1960's, however, Tango popularity declined in Argentina. The military dictatorship had imposed curfews and restrictions on "gatherings," intending to stifle political unrest, but with the result that many dance venues were shut down or forced "underground." On the world scene, the rise of American and British rock and roll stole the attention of young Argentines, and Tango was relegated to a position as a curious pastime of the older generation.
But in the 1980's, the worldwide popularity of the Broadway shows "Tango Argentino" and "Forever Tango" re-ignited interest in this beautiful and passionate dance. Tango dancing and instruction spread throughout Europe and the United States. Travelers went to Argentina to study and learn in the "homeland," and the wave of popularity has been growing ever since.
The situation today is again one of great change. New dance philosophies and styles are being created and developed. New ways of analyzing old steps, and incorporation of new steps and movements from modern dance forms as diverse as Swing and Contact Improvisation are creating a period of rapid evolution. As always in such times, there is much disagreement and often passionate contention over terminology and whether these new principles are true enough to the historical base to even be appropriately called "Argentine Tango." In addition, new Tango music and the practice of dancing Tango steps to other musical forms is popular in many venues but again is often disparaged by those with more traditional philosophies. Only the perspective of history, looking back from some future date, will be able to sort it out.
My personal opinion is that the connection between the partners is the key, and as long as that remains the focus, then you're still dancing Tango.
Unlike most other dance styles, Tango has no fixed rules for tempo or steps. At every beat of the music, the leader has the option to lead the follower to step in any one of several directions (forward, back, side, front-cross, back-cross, weight-change in place, boleo, gancho, etc.), or even to Not step, i.e. to pause. The ability - if not the expectation - to add pauses and tempo changes to accompany the music is a key element making Tango what it is - a dance of infinite variety: no two dances are ever the same. Just as every partner, every song, every night, is different, the dance that results when these unique elements are brought together for this one moment in eternity is itself unique and can never be repeated.
As mentioned above, much of the Tango music that is played in most Milongas was composed in the early part of the 20th century. At this time in the history of Argentina, the largely male immigrant population was yearning for their far-away families and homelands. Their music is filled with the emotion of their loneliness and loss. The plaintive character of the abandoned became the perfect "sound" to express these sentiments of loss. Yet some music, even from those early years, is upbeat and bright, showing an indomitable spirit among the immigrant cultures that were building a life in the new world.
There are three music forms in Tango: "Tango," "Milonga," and "Valz." Tango is the most recognizable form, with 2/2, 2/4, or 4/4 time signature. Milonga has similar time signatures, but is faster. In Milonga, the dancers traditionally step once on every beat, without the pauses common in Tango and Valz (though, as in everything, there are always exceptions, but stepping on every beat is the general rule for Milonga.) The cadence of Milonga is also unique (though it's difficult to describe the character in words), leading to certain step patterns being more appropriate and workable. Valz is "waltz" with a "V". Like waltz, Valz is 3/4 time signature, and has a lilting, flowing character that is different than Tango, which tends to be more thrusting and more dramatic.
Another characteristic of the music is that it's tempo is not always regular. Tempo changes are common, and sometimes there are passages where the "beat" is suspended or imperceptible. While this can make some music challenging to dance to, it also gives the dancers wide latitude in using pauses and rhythm changes to interpret the emotional content that they feel from the music and from their personal moment of reality with this partner, on this dance floor, in this embrace. Pugliese and Piazzolla are good examples of composers of this type of music. Piazzolla has such dramatic tempo changes that much of his music is considered undancable in normal social dances.
Every Step is Led
Social Tango is not choreographed. Every component of every step - timing, speed, and direction - is led. This requires the follower to be paying full attention every moment to the various, sometimes very subtle, body movements that constitute the leader's signals to her. She must suspend all anticipation, expectation, and analysis. She must be balanced and poised, waiting, waiting, waiting to respond to his lead.
The Leader Follows
But the lead-follow dynamic is not one-directional. The leader too must listen and wait for his follower to respond. The leader does not step until the follower has begun to step, until she has committed her momentum. She may not take her step exactly as he had intended. So he must accommodate her, adjusting his step to be in sync with her, so that when the two of them land their steps, they are precisely together.
The follower "paying full attention every moment," and the leader listening to and accommodating his follower, can result in an experience for both partners that has been likened to Zen meditation. The flow of the dance is dictated by the bodily communication between them. It is inherently intimate, on a deep level, and transcends thought and reasoning.
The embrace or "frame" emphasizes and facilitates the connection between the partners. You can dance in "close embrace" style, with full upper-body contact, or in a more open style, separated by some distance. But in either case the center of your chest is almost always facing the center of your partner's chest. Your chests are typically parallel, and the spacing between you, if you're not in close embrace, stays constant. This alignment "aims" your energy and intention towards your partner, committing yourself to him/her for the duration of this 3 minutes of eternity.