Since 8.0 (Godfather) you can find Contract documents in the user interface under the name Agreements & Promotions, located in the Agreements & Promotions menu.
Since 10.0 (Bee’s Knees), there’s also Contract Header Type.
In the diagram you can see the entities used to hold data of the Contract document and their most common fields.
For details about the specific entities, please see the respective articles: