Stretch fabrics are also often called knits. They are made from threads looped and interlocked together making them stretchy. When they have elastane (also called spandex or Lycra) added, they can become very stretchy.
These fabrics can be made from a variety of both natural and synthetic materials including cotton, wool, polyester, modal and nylon.
You can get 2 way stretch, which is across the fabric only, or 4 way which is horizontal and vertical. The percentage will tell you how stretchy the fabric is. A fabric said to have “good recovery” will spring back into shape more easily.