verbal arithmetic; cryptarithm; alphametic
A mathematical puzzle where digits are replaced by letters or symbols, and the solver must deduce the original digits. Common in recreational mathematics and logic puzzles.
In a cryptarithm, the same letter stands for the same digit.
SEND + MORE = MONEY is a famous example of a verbal arithmetic puzzle.
From 覆面 (mask, disguise) + 算 (calculation), referring to digits being masked by letters or symbols.