In the context of aviation and aerospace, "alphanumeric" refers to a type of code or identifier that consists of a combination of letters (alphabetical characters) and numbers. These codes are used to convey specific information, such as aircraft registrations, flight numbers, or navigation data.

In aviation, alphanumeric codes are commonly used for:

1. Aircraft registration numbers: A unique combination of letters and numbers assigned to an aircraft, such as "N12345" or "G-INFO".
2. Flight numbers: A combination of letters and numbers used to identify a specific flight, such as "UA123" or "DL456".
3. Navigation waypoints: Alphanumeric codes used to identify specific navigation points, such as "JENNY" or "LIZZY".
4. Air traffic control clearances: Alphanumeric codes used to convey clearances, instructions, or other information from air traffic control to pilots, such as "Cleared to land on runway 27L" being shortened to "C27L".

In aerospace, alphanumeric codes are used for similar purposes, such as:

1. Spacecraft identifiers: Unique combinations of letters and numbers used to identify specific spacecraft, such as "ISS" or "HST".
2. Launch vehicle designations: Alphanumeric codes used to identify specific launch vehicles, such as "F9-123" or "Ariane 5GS".

The use of alphanumeric codes in aviation and aerospace allows for efficient and unambiguous communication of critical information, reducing the risk of miscommunication and improving overall safety.