This is the 215th most frequent Lithuanian word.
jums
"Jums" means "to you" or "for you" (plural or formal singular).
In this sentence, 'jums' is the dative form of 'jūs,' which is the second person plural or formal you, used to indicate the person enjoying or liking the action.
Ar jums patinka keliauti?
Do you like to travel?
Here, 'jums' is also in the dative case, indicating the recipient of the letter.
Šis laiškas skirtas būtent jums.
This letter is meant specifically for you.
Yet again, 'jums' is in the dative case, identifying the beneficiary of the action of helping.