Recently, South Korea has been making headlines with its own fighter development program – the KF-X. The aircraft developed during the program has been christened the KF-21, and is currently awaiting its maiden flight. It is debatable whether the aircraft really is fifth-generation as it lacks some crucial new generation features, such as internal weapon bays and supercruise ability. However, there are some next-gen staples the KF-21 has in spades: stealthy design, advanced avionics, and a propensity to be much talked about.

I agree, probably a cheap copy of those aircraft.

I think "K" stands for Korean and "F" for fighter plus the number, in this case 21.