As christianity coopted old slavic gods into its own duplicate/replicate saints, so were the house gods replaced with patron saints, and their day in the calendar became the slava (i.e. celebration/glory). It's the day when the family makes a feast for any friends or relatives who would come (by invitation, usually, but then there are those who'd be assumed to not need one).
While in socialist years these were frowned upon (but not illegal - it's a private party) and a possible cause for a party member to lose membership, in Sloba's times and later it became a fashion to overdo it, get seriously drunk and whatever follows.
As a firm unbeliever, I don't do this, but attend those of my own family (that is, only dad's while he was alive).