Trial can mean a few different things:

1. A formal examination in a court of law where evidence is presented and a judge or jury decides if someone is guilty or innocent of a crime, or who is right in a disagreement. During a criminal trial, prosecutors try to prove someone broke the law while defense attorneys argue they didn't. People accused of crimes have the right to a fair trial where they can defend themselves. A jury trial includes citizens who listen to evidence and decide the verdict together.
2. A test to see if something works, or an attempt to do something. When a soccer coach holds tryouts, players may get a trial period to show their skills. Scientists run trials of new medicines to see if they're safe and effective. You might ask for a trial period before buying software to test whether you like it. When you try something new, you're giving it a trial run.
3. A difficult experience that tests someone's patience, strength, or character. A long illness might be described as a terrible trial for a family. The phrase trial and error describes learning by trying different approaches until you find what works.