In Japanese, is a military unit and may be literally translated as "", "task force", "division (of ships)", "group" or "wing". The terms "regiment" and "flotilla", while sometimes used as translations of sentai, are also used to refer to larger formations.
The term was used during World War II by the military of the Empire of Japan for Imperial Japanese Army Air Service (IJAAS) and Imperial Japanese Navy Air Service (IJNAS) military aviation units equivalent to a group or wing in other air forces. However, the term had slightly different meanings in the IJAAS and the IJNAS.
An IJAAS Sentai was made up of two to four squadrons (chà «tai). In the IJAAS, two or more Sentai comprised a hikà Âdan (air brigade). In the later stages of World War II, the IJAAS abolished chà «tai and divided its sentai into hikà Âtai (flying units) and seibitai (maintenance units). A sentai commander (sentaichà Â) was generally a lieutenant colonel.
In the IJNAS, a sentai was a larger unit: a Kà Âkà «tai was the equivalent of an IJAAS sentai. Several sentai made up a kantai (air fleet). In the IJNAS, a Sentaichà  was usually a naval captain.
Sentai in the Japanese Navy were prescribed by the document Naval military command No. 10, dated 30 November 1914.
Paraphrased, they were defined as follows:
The is a franchise of Japanese tokusatsu television dramas produced by Toei and TV Asahi that uses the word sentai to describe a group of three or more costumed superheroes who often pilot fictional robotic vehicles to fight kaiju.