Surge suppressors differ from surge protectors in that surge protectors are basically just extension cords with minimal built-in protection (fuses, etc.). That is, the fuse or breaker may trip when voltage exceeds the limit set by the fuse or breaker. Quality surge suppressors, on the other hand, should be designed to clamp the voltage before any damage is done to the computer circuitry. This distinction, however, is complicated by the fact that many manufacturers use the two descriptions interchangeably.
Clamping voltage (or level) is the level of over-voltage required before a device will attempt to suppress that over-voltage. You can think of clamping voltage as the distance between threads in a butterfly net.