'HIIT' originates from English, specifically the phrase 'High-Intensity Interval Training', where 'high-intensity' meant 'very intense' and 'interval training' referred to 'repeated bouts of work separated by rest'.

'High-Intensity Interval Training' developed from earlier 'interval training' concepts (used in athletics and conditioning in the 20th century) and, in popular and scientific fitness contexts from the late 20th to early 21st century, the phrase was abbreviated to the acronym 'HIIT'.

Initially it described the literal training phrase 'high-intensity interval training'; over time the acronym 'HIIT' came to be used as a standalone noun referring to specific workouts, protocols (e.g., Tabata-style), and a general training approach.