What is the code for excision of lipoma left posterior axillary fold?

CPT code is 21556, I am studying for cpc exam, had a really hard time finding the answer to this one so had to google what it meant. I don't really know how I'm supposed to get thorax out of Axillary fold. My test is in four days, don't think I'll pass. But 21556 is the answer in my answer guide.