A tandem bicycle is a bicycle built for two riders, with two seats, two sets of pedals, and two sets of handlebars, all on one extra-long frame. The riders sit one behind the other, both pedaling together to move the bike forward.

The word tandem means “one behind the other,” which describes exactly how tandem riders are positioned. The person in front is called the captain or pilot and controls the steering and brakes. The person in back is called the stoker and helps provide pedaling power but doesn't steer.

Riding a tandem takes teamwork and communication. Both riders need to pedal in rhythm, and the stoker has to trust the captain's steering decisions. When it works well, a tandem can go faster than a regular bike because two people are sharing the work of pedaling. Tandems are popular with families and friends who want to ride together.

You might also hear people use in tandem to mean working together in a coordinated way, like when two teachers plan a project in tandem or when scientists work in tandem on a research problem.