Any material that is used to block the effects of either abrasive-blasting (sandblasting) or acid etching is called a resist.
For acid etching, wax and acid-impervious films and paints are common resists.
For abrasive-blasting, vinyl resists (rubber-like sheets with adhesive on one side) are popular. Photographic resists allow you to blast highly detail images with exceptional accuracy. Liquid, glue-like resists are also available.
Once the acid etching or abrasive-blasting is complete, the resist is removed to reveal the final design.