Mumbo jumbo is something that's meaningless or confusing but pretends to make sense. When sign a contract, you've got to first read a bunch of legal mumbo jumbo.
The phrase mumbo jumbo is often used to describe overly complicated legal wording or ridiculously complicated bureaucracy. If you're stuck all day at the Department of Motor Vehicles standing in lines and signing forms, you might feel like the process of getting a driver's license is nothing but mumbo jumbo. Sometimes people use mumbo jumbo for languages they don't understand, and it comes from the name of a supposed African idol — probably invented.