Celosa translates to "jealous" in English. While jealousy is a common human emotion, this word is particularly interesting because it's the central theme of the song, even appearing in the title "María La Celosa" (Maria the Jealous One).
The song humorously depicts the struggles of dealing with an extremely jealous partner, making celosa a memorable and highly relevant word to the lyrics. It's a great word to learn for understanding relationship dynamics in Spanish music.
This song is a direct message to María, who the singer calls "celosa" [jealous]. He's telling her to stop being so jealous because he's just with friends, and if she doesn't like it, she can leave! He even says, "yo tengo un condón que alcanza para todas" [I have a condom that's enough for all of them], which is a pretty blunt way of saying he's not exclusive to her and there are plenty of other people who want to dance and have fun with him.
He's clearly fed up with her constant scenes and threats, like "que ya no vas a amarme" [that you're not going to love me anymore]. He just wants her to let him be, and if she can't handle it, then she should go. It's a fun, if a bit harsh, song about someone who's tired of a jealous partner and wants to enjoy life without the drama.