A small amount. An amount no larger than what a full baby's bite would be.
While out for food two friends are sharing a 2 liter of Diet Coke. There is enough for one person to finish the bottle in one gulp, however he or she only pours a "a baby bit" and leaves the rest for his friend.

Nick: "Do you mind if I have a 'baby bit' of that diet coke."

Kyle: "Oh, absolutely"

Nick: "Thanks bro, I left you a 'baby bit'
by Basco13 November 7, 2013
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A unit of measurement referring to a small amount. Roughly more than a shot glass full, but less than a cupful.
Davis: Let me getta baby bit o dat tea.
by Funky Cold Medina Sanchez December 25, 2011
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