EXO was the SM Entertainment band that debuted in 2012 with separate Korean and Chinese groups. SM Entertainment introduced the project as two connected units: EXO-K, which promoted in Korean, and EXO-M, which promoted in Mandarin for the Chinese market.
The group officially debuted on April 8, 2012, with the song “MAMA.” Both units released the same material in their respective languages and promoted at the same time in South Korea and China. This dual-market design was unusual in K-pop and was central to EXO’s original identity.
EXO began with twelve members, six associated primarily with EXO-K and six with EXO-M. Several Chinese members later left the group, and the unit system was eventually discontinued, but the original debut concept remains one of the clearest clues in this question. NCT later developed multiple regional units under SM Entertainment, so the wording is best understood as referring specifically to the SM group that debuted with this Korean-and-Chinese two-unit format in 2012.