A "char" is like a nickname for a character. Just like you have a name, like "Sarah" or "Jake", characters in stories or games can have names too. But sometimes, people give characters shorter names to make it easier to talk about them or remember them.
So, let's say there is a character in a story, and her real name is "Penelope". But her friends and family call her "Penny". This is her nickname or "char". It's not her full name, but it's a shorter version that people feel comfortable using.
Nicknames or "char" can also be used in the video games you play. Sometimes, you get to create your own character and give them a name. But maybe you don't like using their full name in the game, or maybe the name is too long to type. That's when you can give your character a nickname or "char" that is easier to use.
So, to sum it up, a "char" is like a short and easy nickname that people use for characters in stories or video games, so they can talk about them or remember them better.