Capital is the total amount of money (and things with a monetary value, like houses or cars) that a person or institution owns. A bank's capital might be in the billions, while your capital barely makes it into the hundreds.
Capital comes from the Latin capitalis, or "head," which some would argue is the command center of your body. Because your head is so important, capital, as a noun and as an adjective, has come to refer to the primary or chief example of something — whether it's money, a letter, a crime, or the national or state seat of a government. It can be easily confused with the American word capitol, which refers to the buildings where government activities take place.