1. Ectomorph
Long and thin (think runner’s build).
2. Mesomorph
Wide shoulders, lean, and muscular. Generally have a small waist (but not as thin as an ectomorph). Naturally athletic, with strong metabolism. Michelle Obama would be an example.
3. Endomorph
Stout, wide hipped, thick-necked. Typically have low metabolism and low energy, and need lots of sleep. Store fat easily.
Most people are a combination of at least two types. It’s not always easy to tell what you are, especially if you’re a combo. A professional (such as a Nielsen Fitness personal trainer) can figure this out using metrics such as wrist and ankle size, limb length, height, how easily you put on (and take off) extra weight, etc.
If it’s not possible for you to be assessed by a professional – or simply if you’re curious! – here’s a pretty good calculator, which uses a series of questions to determine your body type.