TANDEM

'Tandem' is a Latin adverb meaning "at length" or "finally". In English, the term was originally used for two or more draft horses harnessed one behind another as opposed to side-by-side. By extension the term now refers to any team (of machines, animals or people) working together one behind another.
In English, tandem is often used as an adjective in "tandem seating", as in a two-seat aircraft where the two occupants sit one behind the other, or in "tandem bicycle", where the riders are seated similarly. Tandem is also used as a term for the wheels on a semi trailer to balance the weight of a load of freight. In the real estate world it describes items such as parking in lengthwise two-or-more-car garages.
"Tandem" can be used more vaguely to refer to any group of persons or objects working together, not necessarily in line. "In tandem", for example, in politics and business to describe joint plans and ventures. A tandem may also refer to Tandem language learning, a language learning method in which two partners of different mother tongues each help the other learn the foreign language.