This is the 1283rd most frequent Polish word.
jesteś
"You are."
Here, 'jesteś' means 'you are', used to describe someone's role or relationship (second person singular informal).
Jesteś moim przyjacielem.
You are my friend.
In this instance, 'jesteś' is part of a question and signifies the state of 'being' or presence somewhere, directed at someone.
Czy jesteś w domu?
Are you at home?
Here, 'jesteś' is used to express a characteristic or quality attributed to the subject.