Sometimes people can't hear or speak, so they use their hands to communicate instead. When two people communicate this way, it's called sign language.
Contact sign is a specific way of signing that is used by people who are blind or partially blind. Imagine if you couldn't see someone's hands, it would be hard to understand what they were signing. That's where contact sign comes in.
Contact sign involves the person who is signing placing their hands on the hands of the person they are communicating with. This way, the person who is blind can feel the movements of the hands and understand what is being signed. It's sort of like "reading" sign language with your hands instead of your eyes.
Contact sign is a special way for people who are blind to communicate, and it's an important part of making sure everyone can understand and be understood.