This is a low-jargon website, but some words are essential:

Milonga: a tango social, a.k.a. a ‘salon’ [n.b. the same word is confusingly used to describe a type of dance, an ancestor of tango and also popular with tango-dancers]

Practica: a practice session, usually with a teacher present to answer questions and give advice (‘practica’ is pronounced with emphasis on the first syllable)