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Tofu character
(hexbear.net)
I always wondered what a ☐ was called.
Glyph availability
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If an application does not have access to a glyph, the character will usually be shown as the font's .notdef glyph ⟨⟩ which often appears as an empty box, ☐ (nicknamed "tofu" based on the shape), a box with an X in it, ☒, a diamond with a question mark, �, or a box with a question mark in it, ⍰.
The image is from here - What is the technical term for a replacement character if a font does not have a representation - Graphic Design Stack Exchange
the noto font is named after this for having huge glyph coverage and the goal of “no tofu”, and later into roboto on android (for robot noto and Styx song)