Basically Patrick 2

A fat quarter, also known as a FQ, is a unique way of buying a quarter of a metre of fabric, popular with many patchworks and those doing applique.

A normal 0.25m piece would measure 25cm x 110cm while a FQ will measure 50cm x 55cm approximately. Long and Skinny VS Short and Fat, hence Fat Quarter

You may be able to cut a larger shape from the FQ and therefor it provides a more usable piece of fabric. For example if you only need one 18" square then it would be cheaper to buy the FQ than the purchase 0.5m.

There is time involved with cutting, folding and storing them. When you buy one FQ, we can't cut just your FQ, They are always cut in pairs which means that there is a risk associated with the second one, that perhaps no-one will want to purchase the other half. This is why there is a small charge added to the cost of each fat quarter.