It means crumb, crumb, borona, morona, very small thing, trifle, particle. Small parts of bread. This term is used like this, in Costa Rica.
I live in Carthage Costa Rica Coralillo and here in my town or the area the burusca Word is something very small, anything can be. If they were bread crumbs then well you could say there are buruscas of pan, bone is a basurilla