Entry 1 sense Webster, 1913 bacteriophage · IPA /bækˈtɪəɹ.ɪəʊˌfeɪd͡ʒ/ 01 n. sing. & pl. a virus which infects bacteria; -- also colloquially called phage in laboratory jargon. 1. a virus which infects bacteria; -- also colloquially called phage in laboratory jargon. Also: phage