Halfwidth vs. Alphanumeric: What's the Difference?

Halfwidth and Alphanumeric Definitions
Halfwidth
Of a text character, occupying the space of half of a fullwidth character, or one "normal" text column.
Alphanumeric
Consisting of both letters and numbers.
Halfwidth
(chemistry) The width of a spectroscopic peak at half its height.
Alphanumeric
Consisting of or using letters, numbers, punctuation marks, and mathematical and other conventional symbols
An alphanumeric code.
Alphanumeric
Consisting of, or limited to, letters and/or numbers, especially the characters A to Z (lowercase and uppercase) and 0 to 9.
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Alphanumeric
Consisting of these characters plus punctuation and other special characters.
Alphanumeric
An alphanumeric character.
Alphanumeric
Of or pertaining to alphanumeric characters