what does a red tip on a bullet mean?
It could be several things. Tracer bullets usually do have red tip on them. Many of the Hornady rounds also have red tips, usually plastic. I have seen some cheaper bulk ammo that had some sort of a red dye on the bullets. Many balistic tip bullets have a pointed plastic tip on them that is sometimes colored red.
You’ll need to give more info, possibly even a picture if you want an accurate answer as to what the one you are looking at is.
Red bullet tips