This is the 954th most frequent Spanish word.
estuvieron
"Estuvieron" means "they were" or "you (plural) were" in the preterite tense.
Here, 'estuvieron' is used as the past tense form of 'estar' to indicate a location where they were.
Ellos estuvieron en la casa toda la tarde.
They were in the house all afternoon.
Here, 'estuvieron' suggests a temporary emotional state, linked to the past event.
Estuvieron contentos durante la celebración.
They were happy during the celebration.
In this case, 'estuvieron' is used to describe a condition of being busy at a certain past moment.