I've always had this hard lump at the bottom of my sternum. Why is it there?

Lump at end sternum. Sternum, after all growth centers have fused, has a pointed lower end called the xiphoid process, which sometimes feels like a hard lump. If it is red, swollen, painful, have your doc examine it. If you've ever received cpr, sometimes the xiphoid can be broken due to hand misplacement.