A complete binary tree is a binary tree in which all levels, except possibly the last, are completely filled, and all nodes are as far left as possible. In other words, every level of the tree, except the last one, is completely filled with nodes, and any unfilled positions in the last level are filled from the left side.

  A full binary tree, on the other hand, is a binary tree in which every node has either zero or two children. This means that every internal node (non-leaf node) must have two children, and every leaf node (node with no children) has zero children.

  To summarize:

  - In a complete binary tree, all levels are filled except the last one, and nodes are as far left as possible.

  - In a full binary tree, every node has either zero or two children.

  It is important to note that a complete binary tree may or may not be a full binary tree. A complete binary tree can have leaf nodes with zero children, while a full binary tree cannot have nodes with only one child.