Incantation

From Harry Potter Wiki

The incantation of a spell is what you recite to make it work. Spells can be cast non-verbally but the incantation still needs to be said in the head of the spellcaster.
Most known incantations derive from the latin language but there are a few which are english. Whether not english speaking wizards use the same incantations or have incantations in their own language is not known, since there are no incantations mentioned used by the french and bulgarian students of Beauxbatons and Durmstrang (during the Triwizard Tournament) or by any of the few foreign wizzards (e.g. Igor Karkaroff) mentioned.