Ectomorph: Naturally skinny, low bodyfat, narrow waist and shoulders. Skinny legs. Finds it hard to gain weight without AS.

Mesomorph: Naturally musular. Thicker arms and legs. Tends to put muscle on more easily.

Endomorph: Naturally fat, higher bodyfat. Round shape. Tends to put on weight as fat.

I'm a combination of a mesomorph and an ectomorph. I'd say 80% mesomorph, but my metabolism will hit skids where it burns calories like there's no tomorrow.