yea agreed with bekindbud,
Nitrogen deficiency. but theres things that we gotta know to be 100%, flowering/veg state? when did you feed it last? dirt/hydro? whats the entire plant look like? are there other leaves with 3 fingers like that? the size of those, id guess and say they are a lil deformed/mutated. whats the pH? whats the soil like? temps?
I mean you cant post 1 pic of 1 leaf and expect us to answer your "whats wrong" we need info!