petiole = the little bit of stem connecting the leaf to the stem of the plant more or less.
dont toss it, w/e it is... is clearly not devastating. its probably just deficient. idk why but so many chili folks treat chillies like delicate little orchids or some thing... they are NOT intolerant to fertilizing... they love to be fed. they are NOT delicate little plants that will die if you water twice in a day... they are hardened agricultural plants. they may not be as hardy or vigorous as toms or cuces or w/e but they are not as weak as people seem to think.
feed it a good balanced nutrient solution with decent runoff and watch what it does.
N, P, K and Mg are mobile elements, hence why they manifest in oldest leaves. they will activly translocate from tissues of old leaves to new leaves, leving behind a messed up leaf like that. metals calcium and w/e else are immobile their deficiency will manifest on the newest growth.
edit: wierd font issue.