This is the 11351st most frequent Catalan word.
trobats
"Found" or "discovered."
The word 'trobats' here is a past participle used in a relative clause to describe 'llibres' (books) that were found.
Els llibres que heu trobat són molt antics.
The books you found are very old.
In this sentence, 'trobat' works in the past tense to indicate the action of finding someone.
Ens han trobat jugant al parc.
They found us playing in the park.
Here, 'trobat' functions to indicate the result of the children's action—their discovery of a treasure.