X21 (disambiguation)
X21 may refer to:
- Northrop X-21, an experimental aircraft
- SA-X-21 or S-400 (missile), a Russian anti-aircraft weapon system
- X.21 (sometimes referred to as X21), an interface specification for differential communications
- X21 (band) (次世代ユニット), a Japanese girl idol group
This disambiguation page lists articles associated with the same title formed as a letter–number combination.
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