Pared vs. muro vs. muralla

The Spanish language has multiple words for 'wall', including 'pared', 'muro', and 'muralla'. Each word can be used in slightly different contexts to refer to distinct types of walls.

Pared

A wall within a house or building, which separates rooms from each other. This type of wall cannot usually stand on its own without the structure of the building.
La pared de mi habitación es azul.
(The wall of my room is blue.)
Vamos a colgar el cuadro en esa pared.
(We are going to hang the picture on that wall.)

Muro

A strong and robust wall that can stand independently, usually found on the outside of buildings. It is also used to refer walls used for boundaries or separators like garden walls.
El muro del jardín está cubierto de hiedra.
(The garden wall is covered in ivy.)
Hay un muro alrededor de la casa para la seguridad.
(There is a wall around the house for security.)

Muralla

Refers specifically to defensive walls, like those found around a castle or city. It denotes a large, imposing structure with a purpose of protection and defense.
"La Muralla" es una famosa canción tradicional china.
('The Great Wall' is a famous traditional Chinese song.)
La antigua muralla de la ciudad aún se conserva hoy en día.
(The old city wall still stands today.)

Summary

'Pared', 'muro' and 'muralla' are all Spanish words that can be translated as 'wall'. However, they refer to different types of walls. 'Pared' is typically an interior wall within a building, while 'muro' refers to an external or boundary wall. 'Muralla' specifically describes large defensive walls, such as those around cities or castles.