The term 'SPEED UNIT JET' can be broken down into four parts: 'SPEED', 'UNIT', 'JET', and 'MACH'. The word 'SPEED' refers to the rate of motion, or how quickly something is moving. The word 'UNIT' is a measure of a quantity, such as miles per hour or kilometers per hour. The word 'JET' is a type of aircraft that is capable of reaching high speeds. Finally, the word 'MACH' is a UNIT of SPEED equal to the SPEED of sound in air, which is approximately 1, 225 kilometers per hour.