There are three main types of oats used to create oatmeal. Each of them is derived from oat groats, which are then processed into the various forms we recognize. Steel-cut oats: this type of oat is actually the whole oat groat that's been cut into several pieces. It looks more like grains like rice or barley than the typical soft oats we're used to. This type of oat is the least processed. However, it also takes the longest to cook (up to 40 minutes!) and requires more liquid. Rolled oats: also referred to as old-fashioned oats. These are the most common oats and are the oat groat steamed and rolled into thin flakes that are much faster to cook. These will cook creamy but still have some bite. Quick-cook oats: also referred to as instant oats. These are actually basically rolled oats that have been cut down to smaller pieces, thus taking a shorter time to cook. Due to the smaller pieces, the texture will also change as it is creamier, with less 'bite.'