Leaf Scar: The scar remaining on a twig after a leaf falls.*
The shape of the leaf scar, its relation to the new buds, and the number and position of bundle traces it contains are all important characteristics to look at when identifying trees in winter.
Image credit: Wikimedia Commons
*Harris, J.G., Harris, M.W. (2001). Plant identification terminology: An illustrated glossary (2nd ed.). Spring Lake: Spring Lake Publishing.