We use 'acoustic night' as the general public wording here at the Plough and Fleece near Cambridge UK as we get a mix of tunes and songs. On the folk websites we always refer to it as a 'singaround' as that is the best description for people who know the jargon, For some reason we refer to it amongst ourselves as the 'session' despite knowing full well that would usually mean a tunes dominated night. However, we also use the general expression 'fancy a session at the pub?' meaning a chat and a few beers. Horses for Courses, as we say over here.