It's a limit on shock or strut travel. Although most people are unaware of it, your vehicle's suspension is hitting the bump stop regularly in daily driving. Its a hard disk or cone of synthetic rubber; it gets banged on regularly, and takes a beating but keeps on ticking. If it gets cut or deformed, it no longer does it's job, suspension travel can increase beyond what the shocks / struts are designed to handle, and if they fall out completely, now everything is banging against the metal where the bump stop used to be.
They are inexpensive, or should be, so replacing them should not be a big deal. Check condition when you do shocks / struts.