Punts are long, narrow flat-bottomed boats with square ends.
One propels them along the river by pushing against the bottom of the river with a long wooden pole. Punt' is both noun and transitive verb. In the summer, the river Cam is congested with inept tourists who pay their money to hire a punt and go straight out onto the river with their punt and punting pole. It's really quite funny to see them zig-zagging from bank to bank, falling in and whatnot. Punting's not very difficult, but it does take some practice.