What is the modifier that is to be used when a procedure was begun but had to be discontinued because of deterioration in the patients condition

What is the modifier that is to be used when a procedure was begu…?

http://www.chacha.com/question/what-is-the-modifier-that-is-to-be-used-when-a-procedure-was-begun-but-had-to-be-discontinued-because-of-deterioration-in-the-patients-condition

Could you clarify the term modifier? By the way, incision and drainage is the primary therapy for cutaneous abscess management!