Bacteriophage literally means bacteria eater, because they infect bacteria and kill them.
Bacteriophages aka Viruses are obligate parasites and are made of genetic material surrounded by protein structure.
They need a host for the vital molecular processes like replication, transcription, translation and multiplication.
Once, the virus infects the bacteria, the virus takes the command of all bacterial molecular processes.
The bacteriophage that infect and cause death of the host are called virulent phage.
The viruses that get associated and become part of the host are called temperate phage.
Following infection, the bacteriophage hijacks the bacterium’s cellular machinery to prevent it from producing bacterial components and instead forces the cell to produce viral components.
Eventually, new bacteriophages assemble and burst out of the bacterium in a process called lysis.