Money

Money is the currency used in Guild Wars. There are two denominations of money, gold and platinum. One unit of platinum is worth 1000 units of gold.

Terminology
People refer to gold often as simply "g"/"G" (as in "540g") or just omit it all together (e.g. WTS yellow dye for 200). Platinum is referred to as "p", "plat", or "k"/"K", the latter being because k represents 1000 (e.g. 'WTS silver dye for 8k).

Obtaining money
Money is often obtained by loot, which is dropped by monsters in the PvE part of the game. Also items in your inventory may be sold to other players or merchants.