Afición vs. hobby vs. pasatiempo

In Spanish, the words 'afición', 'hobby', and 'pasatiempo' are all related to activities people enjoy in their free time. However, they have subtle differences in usage and connotation.

Afición

'Afición' refers to a strong interest or passion for an activity. It often implies a deep commitment and long-term dedication.
Tengo una gran afición por la fotografía.
(I have a great passion for photography.)
Su afición por el ajedrez lo llevó a competir profesionalmente.
(His passion for chess led him to compete professionally.)

Hobby

'Hobby' is a loanword from English, used in Spanish-speaking contexts to refer to casual leisure activities. It is often seen as more trendy or modern.
Mi hobby es coleccionar cómics antiguos.
(My hobby is collecting old comics.)
Ella tiene muchos hobbies, como pintar y tocar la guitarra.
(She has many hobbies, like painting and playing the guitar.)

Pasatiempo

'Pasatiempo' literally translates to 'pastime' and denotes activities done primarily to pass the time. These activities might be less intense or passionate than hobbies or aficiones.
Leer libros de misterio es mi pasatiempo favorito.
(Reading mystery books is my favorite pastime.)
El sudoku es un buen pasatiempo para largas esperas.
(Sudoku is a good pastime for long waits.)

Summary

'Afición' conveys a deep passion and long-term interest in an activity, while 'hobby' is used for casual, fun-spirited leisure activities—often perceived as modern or trendy. 'Pasatiempo' focuses on activities intended mainly to fill free time without necessarily implying a strong commitment.