leaf node (of a tree)

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A leaf of a tree is any node which has degree of exactly 1. Put another way, a leaf node of a rooted tree is any node which has no child nodes.

\xymatrix{&\bullet\ar@{-}[dl]\ar@{-}[dr]&&&\inner@par{\color[rgb]{1,0,0}% \bullet}&&\bullet\ar@{-}[dr]\ar@{-}[dl]&&\inner@par&\bullet\ar@{-}[dl]&&{% \color[rgb]{1,0,0}\bullet}&\inner@par{\color[rgb]{1,0,0}\bullet}&&&&}

Figure: A tree with leaf nodes highlighted in red.