SPST = Single-Pole, Single-Throw. This relay has two terminals (hookup points) and switches one circuit on and off.
Normally open type.
Specifications:
| Coil voltage: | 5VDC |
| Coil resistance: | 250 ohms |
| Contact rating: | 0.5 AMP at 125VAC |
| Nominal current: | 20mA |
| Overall length: | 1 inch or 25.4mm |
Your nearby RadioShack store has a wide selection of relays to do the job right, and there's even more available online.