Halfwidth vs. Alphanumeric: What's the Difference?

Of a text character, occupying the space of half of a fullwidth character, or one "normal" text column.

Consisting of both letters and numbers.

(chemistry) The width of a spectroscopic peak at half its height.

Consisting of or using letters, numbers, punctuation marks, and mathematical and other conventional symbols

Consisting of, or limited to, letters and/or numbers, especially the characters A to Z (lowercase and uppercase) and 0 to 9.

Consisting of these characters plus punctuation and other special characters.

An alphanumeric character.

Of or pertaining to alphanumeric characters