Sewing patterns will commonly refer to fabrics as having either 1 way, 2 way or 4 way stretch. Some companies will have a different method but here at Super Cheap Fabrics, here is how we classify a 1, 2 or 4 way stretch.
The first thing to note is that all fabrics will have stretch along the bias or diagonal of the fabric, no matter the type.
1 WAY
This will have stretch along either the vertical or horizontal part of the fabric.
2 WAY
This will have stretch along both the vertical and horizontal part of the fabric.
4 WAY
This is the same as a 2 Way, but it just makes reference to the inherit stretch along the bias/diagonal part of the fabric which is part of all fabrics!
So, in conclusion - we refer to fabrics as having 1 or 2 way stretch. If your pattern says 4 way stretch, you need to look for a 2 way fabric.
Here's a little video by Zerrin further explaining this and showing some examples: https://www.youtube.com/watch?v=L4h49RC9oEU&t=36s