Your hair type is based on your hair texture. Hair is categorized into four types: straight, wavy, curly, and coily. Black people's hair tends to fall into the last two categories, so we'll focus on those two. With those hair types there are subtypes, a, b and c, that describe your curl pattern.
Curly hair is usually referred to as type 3 hair. The strands of hair are looser.
Coily hair is usually referred to as type 4 hair and the strands are tighter.
To find out more about the the subtype of each hair type, you can visit this site Hair types