Take comfort in knowing that most bumps and lumps that people find are completely benign!
Does it feel soft and roll around easily? It could be a lipoma, which is just a harmless, fatty bump!
It could also be a cyst. Cysts can form anywhere!
Is this lump hard or soft? Is it mobile or fixed? Does it feel rough or smooth? How long has it been there? Is it actually painful or not (i.e. have you been prodding it enough to cause it to hurt or is it hurting on its own accord)?
For peace of mind and a proper diagnosis, I would suggest seeing a doctor. Not to worry though - like I said, most bumps are benign, and there are many things that could cause it.