Códigos (Codes)
Códigos (codes) are the dance etiquette that developed over the years in the milongas of Buenos Aires. To people seeing the códigos for the first time, it may seem like a frustrating, long list of rules to be memorized. But those that take to time to review them will find that they are all common sense and will help dancers through unfamiliar situations with ease.
As milongas (tango dance parties) 
transitioned from live orchestras to music played by a DJ, a tradition evolved of playing music in sets, called tandas, separated by cortinas (literally “curtain,” like the closing of the curtain between acts of a theatrical play). Tandas are sets of 3 or 4 songs played by one orchestra. Tango tandas are usually 4 songs, while Vals and Milonga tandas are 3 songs. Tandas normally consist of music from the same orchestra, in the same era, and the same singer if there is one. This gives the dancers assurance of what music will play throughout the tanda. The cortina between tandas is a short piece of non-tango music.