Body type is relevant to health, exercise, and appearance. It's worth bearing in mind that few people are a pure type, and that, for example, endomorphs can be fat (often termed "skinny fat" - ie a belly on a slender frame) and ectomorphs are not necessarily fat.
The body types are genetic, products of inborn bone and muscle structure. In other words, the body frame.
Your body type has implications for strength and fitness training - and for strength and fitness goals. 3 Male & Female Body Types Explained