A mass of histologically normal tissue found in an abnormal anatomic location is called a:

A choristoma is normal tissue in an abnormal location (e.g., gastric or pancreatic tissue found in the floor of the mouth). A hamartoma, by contrast, is a disorganized excess/overgrowth of tissue that normally belongs in that location. Teratomas contain tissue from multiple germ layers, and a neoplasm is uncontrolled cellular proliferation that may or may not resemble normal tissue.