So imagine you're playing a big game of tag with your friends, and you're on the losing team. You really want to win, and you're willing to do anything to try and catch the other team.
A banzai charge is a little bit like that, but with soldiers in a war. Sometimes, when one group of soldiers is losing a battle, they might decide to do a banzai charge. That means they all run really fast towards the other side, even though they know it's dangerous and they might get hurt or killed.
They do it because they hope that by being brave and surprising the other side, they might be able to win the battle after all. It's like a last-ditch effort to turn the tide of the war.
Although banzai charges can be very brave and show a lot of determination, they can also be very dangerous and often result in a lot of casualties. So they are generally not recommended as a good tactic to use in war.