A dansa viva (live dance) is one performed at a specific point in a specific festival. They are usually performed at key moments, when the ritual aspect is more explicit.
Often the dancers do not have any specific training, not will they repeat the dance in question. The way they get to take part varies from place to place: maybe through a draw, maybe because they have just got married, maybe because they have a particular job, etc.
Another characteristic of these dances, generally speaking, is they are held in a street or a square. Keeping clear of the stage significantly reduces the idea of a show in favour of the idea of a ritual.
In Catalonia the dansa viva heritage is as rich and extensive as it is unknown. The most popular kinds include the jota, the sardana, etc.
Barcelona is not particularly rich in them but does have some worthy of mention, for example, the Ball de Rams d’Hostafrancs and the Galop de la Mercè.