Attrition is defined as the termination of the employment.This term refers to the voluntary and involuntary terminations, deaths and employee retirements that result in a reduction to the employer’s physical workforce. If you work in a human resources department at a large organization, keeping track of attrition trends can be a job in and of itself.
It means inflicting casualties on the other side after they inflict casualties on you. Two armies bleeding each other. An analogy would be two people sitting by a pond. One has ten pebbles the other one has 15. Every time one of them throws in a pebble the other person has to throw one in the pond too. The one with some pebbles left afterwards wins. In war, you attack the enemy and he retaliates by attacking you until one side runs out of soldiers. That is a war of attrition.