A seabird is any bird that lives most of its life near the sea (makes sense, right?). Gulls are one of the most common types of seabird.
When you go to the beach, you're bound to sea at least some seabirds. The big gray and white seabirds that try to steal your lunch are gulls, and the tiny seabirds that look like wind-up toys running in a group along the tideline may be plovers. Most seabirds nest in large colonies, and most of them are also migratory, meaning they travel many miles during the course of a year, often circumnavigating the entire planet.