Can refer to a belt or a type of supportive garment.
Siempre uso una 'faja' para sentirme más cómodo y apoyar mi espalda.
I always wear a 'belt' to feel more comfortable and support my back.
Decidí comprar una faja nueva para sentirme más cómoda durante la fiesta.
I decided to buy a new belt to feel more comfortable during the party.