literally, "kill it!" It is usually an interjection. It comes from the Spanish verb, "matar", which means, "to kill." the lo is a direct object pronoun used for masculine objects. The pronoun "la" is used for feminine direct objects. You can also say "matale" which means not only kill him, but also her. Gender doesn't matter in that instance.

Got the covid-19 vaccine

What them niggas in Resident evil 4 say to each other to threaten Leon.