Okay kiddo, have you ever waited in line for a really long time? Like at the amusement park or for ice cream? Waiting in line isn't very fun, is it? It's the same for people who are accused of a crime. They don't want to wait in jail or go to court for a long, long time. That's why we have something called a speedy trial.
A speedy trial means that the government (that's the people who are in charge of making sure everyone follows the rules, like police officers and judges) has to give the person who's accused of a crime a trial within a certain amount of time. Usually, that means within 70 days after they were arrested or charged with a crime. This way, the person accused of a crime doesn't have to wait in jail or worry about their case for too long.
It's kind of like saying "okay, we're going to get this over with quickly so you can go back to your life, whether you're guilty or not." But it's important to remember that even though the trial is fast, it still has to be fair. That means the accused person gets to have a lawyer, present their side of the story, and the government has to prove that the person really did the crime.
See, that wasn't so hard to understand, was it? Basically, a speedy trial means that the person accused of a crime gets their trial done fast so they don't have to wait in jail for a long time.