A toggle switch can be used as a simple on-off switch, but also to choose between two voltages or signals.
Toggle switches can have as much as 4 change-over contacts.
Terminals refer to physicals contacts on the switch which can be either multiples of 2 (on-off) or multiples of 3 (left, center, right).
Pole refers to the number of signals controlled by the switch: SP (Single Pole) switches control only one electrical signal. DP (Double Pole) switches control two independent signals (and act like two identical SP switches that are mechanically linked). Do not confuse ‘pole’ with ‘terminal’. The DPST switch, for example, has four terminals, but it is a DP, not a 4P switch.
Throw refers to the extreme position of the handle: ST (Single Throw) switches close a circuit at only one position. The other position of the handle is Off. DT (Double Throw) switches close a circuit in the handle left position, as well as the handle right position (On-On). A DT switch can also have a center position (frequently On-Off-On).
Single pole/throw and double pole/throw switches are by far the most common switches, but triple and quadruple configurations are also available. They are commonly denoted 3PST, 3PDT, 4PDT, etc.
The switch in the illustration has 3 terminals and is a single pole, double throw switch (SPDT).
Rated voltages and currents differ per type of switch.