NCT 127 is the second sub-unit of NCT. They debuted on July 7, 2016 on M Countdown with their debut stage for "Firetruck", the title track from first mini album, NCT #127, which was released on the 10th.
The number 127 refers to the longitude for Seoul, where they are based.
On January 6, 2017, the group made a comeback with two new members, Johnny and Doyoung. On September 17, 2018, Jungwoo was announced as a new member of the unit.