Cadastres are official maps showing the location and boundaries of parcels of land. Properties can cover anything from one to several hundred parcels, all uniquely numbered on a cadastre. You can now see them on-line on a slow government site (and order hard copies), www.cadastre.gouv.fr
These maps are invaluable when buying and selling property. Make sure you understand which parcels you are buying and that they appear explicitly in the Act de Vente.
Incidentally you will pay an annual tax on each parcel you own, depending on how it is classified (aggricultural, scrub, woodland, etc)
On th right is a small piece of a sample Cadastre - This is a small section of a Cadastre sheet. There are typically several sheets for each commune.