At milongas and practicas we dance three or four songs with one person – this is called a “tanda”, sometimes separated with 15-30 seconds of contrasting music, called a cortina (curtain). If there is no cortina, you can just count four songs.
Tandas are usually songs of the same type. There are three types of tango music: tango, vals (waltz), and milonga. Milonga is the fast one. The tanda may also be a group of music by the same composer or in the same style or era. So you get a whole tanda of milonga music, or vals, or tango music with a certain feeling.
Leaders often wait to hear the type and style of music before deciding to dance and selecting a partner.
Generally, once we have agreed to dance, we complete the tanda of four dances with that person. It is considered rude not to complete the tanda. We do not break the tanda because of the person’s dancing skill. There are, however, times when we do break the tanda despite the fact it is rude. That would be: if the person is running into people (or furniture) a lot and you feel unsafe or unprotected dancing with them; if they are groping you or making you very uncomfortable in a way that is not part of the common tango embrace; if they are drunk, which is considered unacceptable in tango. Generally, sweatiness and other discomforts that are simply a result of being close to another person is accepted in tango, and we do not break a tanda for these kinds of discomforts.
See the Etiquette Guide for more details on the milongas, the cabeceo, and tango’s codigos.