Symbols pipe ( | ), colon ( : ), and underscore ( _ ) characters mean in naming...

Pipe separates hierarchies. Each hierarchy is represented by the module/entity and the instance, separated by a colon. So you might have something like:

top|rf:rf_A|filter:filt_inst|free_count[3]

So top instantiates an entity/instance called rf with instantiation rf_A. Then filter is instantiated, and within that is a register called free_count, and this is bit 3. The underscores are added by the user, but can also be added during synthesis if something gets resynthesized(although I think Quartus often adds ~, i.e. it might be free_count~RESYNTH323432 as a new name if it gets resynthesized. It depends.