Cabelo vs. pelo
In Portuguese, both cabelo and pelo can be translated as hair, but they are not interchangeable. The main difference lies in where the hair is located: cabelo refers to the hair on the human head, while pelo is used for body hair, animal fur, and other fine fibers.
Cabelo
A1Cabelo specifically refers to the hair that grows on a person's head. It can describe the entire head of hair, a single strand from the head, or a person's hairstyle.
Ela tem um cabelo comprido e loiro.
(She has long, blond hair.)
Eu preciso cortar o cabelo esta semana.
(I need to get my hair cut this week.)
O cabelo dele é muito cacheado.
(His hair is very curly.)
Encontrei um fio de cabelo na minha sopa.
(I found a strand of hair in my soup.)
Vou pintar o meu cabelo de vermelho.
(I'm going to dye my hair red.)
Pelo
A2Pelo is a broader term used for hair on the human body (excluding the head), the fur or coat of an animal, and the fine, fuzzy fibers on surfaces like fruit or fabric.
Ele tem muito pelo nos braços e no peito.
(He has a lot of hair on his arms and chest.)
O pelo do meu gato é muito macio.
(My cat's fur is very soft.)
O cachorro está a perder muito pelo no verão.
(The dog is shedding a lot of fur in the summer.)
O pêssego tem um pelo fino na casca.
(The peach has a fine fuzz on its skin.)
Este tapete tem o pelo muito curto.
(This carpet has a very short pile.)
Summary
In short, use cabelo for the hair on a person's head and pelo for almost every other type of hair or fur, including human body hair, animal coats, and even the fuzzy texture on a peach. A simple rule is: if it's on a human head, it's cabelo; otherwise, it's most likely pelo.