Height of a binary tree is the longest path from it’s root to any of its leaves.
With number of nodes as n,
Max height possible: n-1 (skewed binary trees)
Min height possible: $floor(\log_{2}n)$ (perfect binary trees)
An AVL tree is a height-balanced binary tree where the difference between the heights of the left subtree and the right subtree cannot exceed 1 for all nodes.