Answer:
If you lose me, you may cause people around you to lose me too. What am I?
I belong to you but others use me more often than you do. What am I?
I am there when you sit, but gone when you stand. What am I?
I am in the middle of water but am not an island.
Until I am measured, I am not known. Yet, how you miss me when I have flown. What Am I?
What language does a billboard speak?