I have a large round lump on the back of my neck it doesn't hurt and it moves if pressed on. is this a sign of a serious condition or is it cosmetic?

Lipoma or cyst: The most common causes of a painless soft lump in that area are lipoma (a benign fat tumor) and epidermal cyst (a benign cyst that forms when cells from the top skin layer go deeper). If it's large, it's probably been there for a long time - so i would suggest seeing your doctor, who will make sure it is not something more unusual and potentially more of a problem.

Not sure unless seen: This is probably a benign cyst or lipoma, but without evaluation by an expert (general surgeon, ent, or plastic surgeon), it is impossible to give you honest reassurance. Plus, it won't go away on its own, and may get larger! so, why delay getting it dealt with? Insurance may cover its removal, usually under local anesthetic as a quick outpatient procedure. But what if it's something bad? Be seen!