It is the singers equivalent of a Session and at festivals, the two are normally run separately and often at the same time. This keeps singers out of sessions and gives them a place of their own.
Note that there is a persistent and annoying trend to use the terms 'Singaround' and 'Session' to mean a gathering where anything may be performed. There is one gathering in Lancashire which is called a Singaround and advertsises:
C'est magnifique, mais ce n'est pas le Folk!