When a sponge, usually a piece of gauze, is left inside a patient during surgery, a fibrous tumor will develop around that foreign mass. That tumor which then contains that foreign object is called a gossypiboma.
Textiloma is a synonym for a gossypiboma.
The word is derived from the Latin word gossypium which means cotton, combined with the word boma which is Swahili for a hiding place. Of course oma also means tumor or abnormal growth in Latin.
If you hear a someone use the word gossypiboma, they are referring to a surgical sponge left inside a patient.