The Twin Zephyrs, also known as the Twin Cities Zephyrs, were a pair of streamlined passenger trains on the Chicago, Burlington and Quincy Railroad (CB&Q), running between Chicago and the Twin Cities of Minneapolis and Saint Paul in Minnesota. It was the second Zephyr service introduced by CB&Q after the record-setting Denver–Chicago "dawn to dusk dash" of the Pioneer Zephyr trainset.

A streamliner is a vehicle incorporating streamlining in a shape providing reduced air resistance. The term is applied to high-speed railway trainsets of the 1930s to 1950s, and to their successor "bullet trains". Less commonly, the term is applied to fully faired upright and recumbent bicycles. As part of the Streamline Moderne trend, the term was applied to passenger cars, trucks, and other types of light-, medium-, or heavy-duty vehicles, but now vehicle streamlining is so prevalent that it is not an outstanding characteristic. In land speed racing, it is a term applied to the long, slender, custom built, high-speed vehicles with enclosed wheels.