Alopecia refers to a medical condition that causes hair loss, either in small patches or all over the body. There are different types of alopecia, including:

Androgenetic alopecia: This is the most common type of hair loss, which affects both men and women. It is also known as male-pattern baldness or female-pattern baldness.
Alopecia areata: This type of hair loss occurs when the immune system attacks the hair follicles, causing hair to fall out in small, round patches on the scalp or other parts of the body.
Alopecia totalis: This is a more severe form of alopecia areata, which causes complete hair loss on the scalp.

Alopecia universalis: This is the most severe form of alopecia, which causes hair loss on the entire body, including the scalp, face, and body.