What is the engraving in the pantheon mean?

it is called inscription. Engravings are images on paper as prints or illustrations produced with the incision of a design onto a metal intaglio printing plate or the decorations on metal or glass objects.

The inscription says: M•AGRIPPA•L•F•COS•TERTIVM•FECIT; that is, Marcus Agrippa, Lucii filius, consul tertium fecit; Macus Agrippa, son of Lucius consul for the third time built it.