Can you tell me what is congenital adrenal hyperplasia in simple words?

Yes: These people have a gene that makes it hard to make the necessary hormone cortisol, and the molecules get shunted into producing masculinizing hormones instead. The adrenals are big. In mild cases, it simply produces extra body hair in women. In severe cases, a little girl's genitals are ambiguous from birth, or a little boy reaches puberty at a very early age.