A sequence of four elements.
One of a group of four, particularly one of four babies born from the same mother during the same birth.
A tuplet of four notes.
A cycle for carrying four riders, arranged so that all the riders can assist in the propulsion.
A set of four works of art that are connected, and that can be seen either as a single work or as four individual works. They are commonly found in literature, film, or video games.
A group of four dramas, three tragic and one satiric, exhibited together at the festivals of Dionysus at Athens.
Tetralogy of Fallot.
A combination of four symptoms.