Diamond carat weight is the measurement of how much a diamond weighs. A metric "carat" is defined as 200 milligrams.
Each carat can be subdivided into 100 'points.' This allows very precise measurements to the hundredth decimal place. A jeweler may describe the weight of a diamond below one carat by its 'points' alone. For instance, the jeweler may refer to a diamond that weighs 0.25 carats as a 'twenty-five pointer.' Diamond weights greater than one carat are expressed in carats and decimals. A 1.08 carat stone would be described as 'one point oh eight carats.'
The modern carat system started with the carob seed. The Carob is native tree to the eastern Mediterranean, probably the Middle East, where it has been in cultivation for at least 4000 years. The carob tree has fruit pods that contain multiple seeds. It was a simple task to get your hand on a bunch of carob seeds of the same size and count on them all to be pretty much the same weight. Or, at least, it was perceived so. The weight of an object was then expressed in terms of the equivalent number of carob seeds. This was standard for commerce and it was even used to weigh things like gemstones and gold. So, naturally, the early gem traders used these small, uniform seeds as counterweights in their balance scales. The carat is the same gram weight in every corner of the world.