otpadak

1. (usually plural) waste; scraps; rubbish
   Otpatke od hrane bacamo u poseban kontejner. — We throw food scraps into a separate bin.
   Posle renoviranja ostalo je puno otpadaka. — A lot of waste was left after the renovation.
2. derog. (of a person) scum; reject
   Takvi ljudi su otpadak društva. — People like that are the dregs of society.

In the sense of waste it is almost always plural: otpaci.