ELI5: Explain Like I'm 5

Complex Lie group

A complex Lie group is like a big playground made up of lots of smaller playgrounds. Each of the smaller playgrounds has its own set of rules, and the way the children play on it can be different too. The bigger playground is made up of all the smaller playgrounds connected together, and the children can play on all of them as a group. It's like an imaginary world where the children get to make their own rules and have fun.