Wikipedia disambiguation page: for "Tofu" mentions: Slang for the empty boxes shown in place of undisplayable code points in computer character encoding, a form of mojibake
"Tofu" is a more recent phenomena, that didn't really have a specific name until now: when there are Unicode code-points—correctly decoded—in a document, but you have no font installed that offers a glyph to represent them.
Mojibake results from "I did this wrong and didn't notice"; tofu results from "I know what this is, and it's something I don't have a visual signifier for."
Mind you, often mojibake will result in "tofu"; the garbage code-points you get from bad encoding detection will turn out to be ones that don't have a currently-defined Unicode character, so they'll show up as U+FFFD REPLACEMENT CHARACTER (�). But that's a coincidence, rather than an equivalence.