The half square triangle unit is probably the most commonly used patch in a quilt block -- well it is second only to the square. It is made simply with two triangles, filling up half the square each -- hence the name. Take a quick look through this website, or in any quilting magazine, and you will start to notice that this half square triangle, regardless of its size, is present in more quilts than not.
Free Quilt Block Pattern
The Depression quilt block was likely created during the time known as the 'Great Depression' in the 20th century. Therefore, it seems likely that this block was made using the quilter's scrap fabric stash. So, the sample block is made in that fashion, using a variety of both lights and dark fabrics.
This is an easy four patch quilt block to make since the only patch used is the half square triangle. Once you master making those, it is simply a matter of the arrangement of the patches to create the block.
All sorts of different quilts can be designed using this one quilt block. By laying the blocks in a straight set or on point, the creativity is endless.