This is the 521st most frequent Hebrew word.
למי
"To whom" or "for whom."
This usage of 'למי' is an interrogative to inquire about the recipient of an action.
למי היא נתנה את הספר?
To whom did she give the book?
Here, 'למי' reflects uncertainty about the recipient in a declarative statement.
אני לא יודע למי לשלוח את ההודעה.
I don't know whom to send the message to.
In this case, 'למי' introduces a dependent clause describing a group of individuals.