Renesmee Carlie Cullen
's nickname, given to her by Jacob Black
because he considers her full name to be a mouthful, though Bella strongly dislikes him nick-naming her child "after the Loch Ness Monster". However all of the characters adopt this shortened version.
*spoiler* Also "Vanessa Wolfe" is actually Nessie. In Breaking Dawn Bella is worried about a possible Volturi
attack, so she gets Fake Id's for Jacob and Nessie calling them Jacob And Vanessa Wolfe
, since Bella assumed that that was a name that "Nessie" could be short for *spoiler*