Referring to something in its original or normal position: In the old abandoned house, the girls found a collection of in situ books on the dusty shelf.

1. Pertaining to where something is found in its original position or place: The old pirate ship was found in situ where it had sunk hundreds of years ago!
2. Not invasive; applied especially to carcinomas which have not invaded beyond their original epithelial confines: The tumorous growth which Dr. Hathaway examined in situ had not spread from its former position in Sandy's body.

Literally from Latin, "in place", an expression used by scholars, who may say, for example, that an observation or experiment was performed in situ, signifying that it was made in the natural or original location of the material or process under study.