Difference between "Complete binary tree", "strict binary tree","full binary Tree"?

Perfect Tree:

       x
     /   \
    /     \
   x       x
  / \     / \
 x   x   x   x
/ \ / \ / \ / \
x x x x x x x x

Complete Tree:

       x
     /   \
    /     \
   x       x
  / \     / \
 x   x   x   x
/ \ /
x x x

Strict/Full Tree:

       x
     /   \
    /     \
   x       x
  / \ 
 x   x 
    / \
    x x 

Wikipedia yielded

A full binary tree (sometimes proper binary tree or 2-tree or strictly binary tree) is a tree in which every node other than the leaves has two children.

So you have no nodes with only 1 child. Appears to be the same as strict binary tree.

Here is an image of a full/strict binary tree, from google:

A complete binary tree is a binary tree in which every level, except possibly the last, is completely filled, and all nodes are as far left as possible.

It seems to mean a balanced tree.

Here is an image of a complete binary tree, from google, full tree part of image is bonus.

There is a difference between a STRICT and FULL BINARY TREE.

1) FULL BINARY TREE: A binary tree of height h that contains exactly (2^h)-1 elements is called a full binary tree. (Ref: Pg 427, Data Structures, Algorithms and Applications in C++ [University Press], Second Edition by Sartaj Sahni).

or in other words

In a FULL BINARY TREE each node has exactly 0 or 2 children and all leaf nodes are on the same level.

For Example: The following is a FULL BINARY TREE:

          18
       /      \   
     15       30    
    /  \     /   \   
  40    50  100  40 

2) STRICT BINARY TREE: Each node has exactly 0 or 2 children.

For example: The following is a STRICT BINARY TREE:

         18
       /     \   
     15       30    
    /  \          
  40    50

I think there's no confusion in the definition of a Complete Binary Tree, still for the completeness of the post I would like to tell what a Complete Binary Tree is.

3) COMPLETE BINARY TREE: A Binary Tree is complete Binary Tree if all levels are completely filled except possibly the last level and the last level has all keys as left as possible.

For Example: The following is a COMPLETE BINARY TREE:

           18
       /       \  
     15         30  
    /  \        /  \
  40    50    100   40
 /  \   /
8   7  9 

Note: The following is also a Complete Binary Tree:

         18
       /     \   
     15       30    
    /  \     /   \   
  40    50  100  40