זֶבַח zebah "sacrifice, offering" sometimes refers to a particular sacrifice:
the covenant sacrifice
the Passover
annual sacrifice
thank offering
but also often in general terms to those animal sacrifices in which some of the meat is eaten by the human participants and some burnt (consumed by God).

In Am 5:25 the plural is likely to refer to sacrifices in general, while at 4:4 (see remarks on that verse) it is likely the word refers to the annual sacrifice.