A liability waiver is a legal document that shields one party from liability for injuries to the person who signs the document. When you sign a liability waiver, you are waiving your right to take legal action against a business for an injury you suffer while patronizing the business.
For example, a liability waiver for a gym/fitness center is designed to shield the business from liability for injuries you suffer while using the facility and equipment in that facility. If you sign a waiver before skydiving, using a trampoline at an indoor trampoline park, ziplining, bungee jumping, rock climbing or some other dangerous activity, the company that sponsors the activity is hoping the waiver will protect them from injury claims.
It is important to note schools and youth organizations often want parents to sign liability waivers when their children go off campus or take part in sporting events.