K21 is a South Korean infantry fighting vehicle.
K21 may also refer to: Vehicles Automobiles Changhe Freedom K21, a Chinese pickup truck
Ships , a frigate of the Royal Navy , a corvette of the Swedish Navy
Aircraft Schleicher ASK 21, a two-seater training glider commonly referred to as the K21
Other uses K-21 (Kansas highway) Gastroesophageal reflux Lactobacillus plantarum strain K21 Uniform k21 polytope "Va, dal furor portata", an aria by Wolfgang Amadeus Mozart