This is also called herpes zoster. It's the same virus that gives people chickenpox. After you've had chickenpox, the virus stays in your system for the rest of your life. Anyone who's had chickenpox can get shingles (but this usually won't happen until someone is an older adult).
Shingles causes a rash with blisters on the body that can be very painful. The blisters are contagious and can spread the chickenpox virus to people who have never had chickenpox and didn't get the chickenpox vaccine.