Kiwanis Club of San Marcos

May...A Riddler's Choice....5/21/18

.........Well, I can tell that the riddles thus far have been way too easy, so here is one that might given you a challenge!
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Riddle last week: "What 'room' has no door, no windows, no floor, and no roof? (Elbow room)
Riddle this week!  "If you have me, you'll want to share me.  But if you share me, I will no longer exist.  What am I?___________?