Currencies are items which can be exchanged and are commonly used for transactions in RuneScape.
Coins (or gold pieces "gp") are the main form of currency and are almost universal, as they are accepted by most NPC's and are the currency used by the grand exchange. All other currencies may only be used at their specific location. Only trading sticks are comparable to gold pieces in that they can be used to buy and sell items in multiple places as well as to trade with other players, although their usage is much more limited than usage of gold pieces.
Here is a list of all currencies which currently exist in the game, and the areas in which they are used:
Dungeoneering tokens, Kudos, Void Knight commendation points, Penguin points, Stealing Creation points, Slayer reward points, Warrior's Guild tokens, and Zeal points are virtual (or kept 'on record'). Thus, these do not take up inventory or bank space.
Pizazz points are stored in a Pizazz hat.