This is the 361st most frequent Greek word.
όλα
"Όλα" means "everything" or "all" in English.
Here, 'όλα' is used as a pronoun meaning 'everything', referring to a collective subject.
Όλα ήταν όπως τα άφησες.
Everything was as you left it.
In this sentence, 'όλα' functions as an adjective modifying 'τα βιβλία', meaning 'all' to denote entirety.
Μου αρέσουν όλα τα βιβλία στη βιβλιοθήκη.
I like all the books in the library.
Here, 'όλα' is again used as a pronoun meaning 'everything', referencing all events or matters related to the trip.