Red team is like a pretend game where some people pretend to be bad guys trying to harm something, and other people pretend to be the good guys trying to stop them.
The bad guys, or the "red team," are usually hired by a company or organization to find weaknesses in their security systems. They try to hack into the organization's computer networks or sneak into their buildings, without getting caught, to see if they can steal sensitive information or cause damage.
The good guys, or the "blue team," are the ones who work for the organization and are responsible for defending against the red team's attacks. They try to stop the red team from accessing the company's information and systems, and then make changes to the security systems to make them stronger.
Overall, the red team is a way for companies to test and improve their security systems, by playing a pretend game where some people pretend to be bad guys, and other people try to stop them.