This is the 54th most frequent Romanian word.
lor
"Their" or "to them."
"Lor" indicates possession and shows that the books belong to 'them'.
Le-am dat cărțile lor.
I gave them their books.
"Lor" shows possession, indicating that the opinion belongs to 'them'.
Opinia lor este validă.
Their opinion is valid.
"Lor" is used as a pronoun to refer to the indirect object, denoting 'them' as the recipients of the thanks.