Fermat is a lunar impact crater located to the west of the Rupes Altai escarpment.

To the west-southwest is the larger crater Sacrobosco, and to the southwest is the irregular Pons.

The north rim is indented by a double crater formation that includes Fermat A.

[1] It is named for 17th century French mathematician Pierre de Fermat.

[3][1] By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Fermat.