Beacon

[1] System of visual lights indicating fixed features, e.g., masts, reefs.
[2] A radio- beacon, which can be of any frequency but is usually very high frequency, and can be omni- directional or of directional beam type.
[3] Vertical fan marker beacons are radio beams used to identify particular spots in control zones and on approach patterns.
[4] A non-directional beacon (NDB) is a transmitter, the bearing of which can be determined only by an aircraft equipped for direction finding.
See also anticollision beacon, instrument landing system