If you're just getting into sewing, you'll often hear the words "fat quarter" thrown around. So, what exactly is a fat quarter? It's a term used to describe a specific cut of fabric - a quarter of a yard of fabric, but cut 'fat' so that it's more useful for cutting out pieces for quilting.
A fat quarter is a term used in quilting to describe a unit of fabric measuring approximately 18" by 22" (45cm x 56cm). Fat quarters are commonly used because they provide a variety of different fabrics and prints in smaller quantities, making it easier for quilters and fabric artists to experiment with different colour schemes and patterns.

The term "fat quarter" comes from the fact that the fabric is cut into quarters, but with the length of the fabric being roughly double the width, thus giving it a "fat" appearance. This shape enables quilters to cut pieces for quilting without lots of waste. Depending on the print of fabric, you may also get more of the design or pattern to work with. Fat quarters are also a convenient size for making small projects such as bags.
Fat quarters are widely available from fabric stores and online retailers. They are typically sold in pre-cut sets that include a range of different prints and colours, or they can be purchased individually.
Is there such a thing as a metric fat quarter?
Yes - if your fabric store sells fabric by the metre, they may cut quarter metre cuts (0.25m) as a metric fat quarter:

The fabric retailer should list on their website if 0.25m is cut straight from the bolt (roll of fabric) or as a fat quarter.