Lysin is an alternative name for endolysins and are hydorlytic enzymes produced by phages. This enzyme is produced to break down the cell wall at the end of the lytic cycle.  This doesn’t end well for the bacteria !

Well written article on Wikipedia discussing the process in depth.  The interesting thing about phage lysins is that they tend to be pretty specifc as to what bacteria they kill.   Ideal to leave in place all those ‘good’ bacteria we live with everyday.