A safety harness is like a special kind of backpack that helps keep you safe when you're doing something like climbing or working up high. It has straps that go around your body and a special buckle that makes sure you don't fall.
Just like when you wear a seatbelt in a car, a safety harness keeps you from moving around too much and getting hurt if you fall. It's really important to wear one when you're doing something high up, because falling from a tall height could really hurt you!
So always remember to buckle up your safety harness and make sure it's adjusted properly before you start climbing or working up high!