The word shingle has two main meanings:

1. A thin, flat piece of material used to cover roofs or walls. Shingles overlap like scales on a fish, creating a protective layer that keeps rain and snow from leaking through. Traditional wooden shingles were split from cedar logs, while modern shingles are often made from asphalt, slate, or composite materials. When you look at most houses, you're seeing thousands of shingles working together to keep the inside dry. Roofers shingle a house by nailing these pieces on, row by row, starting from the bottom and working up.
2. A small signboard hung outside a professional's office. When a doctor or lawyer finishes their training and opens a practice, people say they've hung out their shingle. This comes from the old tradition of hanging a wooden sign outside your shop or office to advertise your services. If you walk through an old downtown, you might still see painted signs announcing “Dr. Sarah Chen, Dentist” or “Thomas Wright, Attorney at Law.”

The roof meaning is far more common in everyday conversation. The signboard meaning mostly appears in the phrase “hang out your shingle,” which means to start your own business.