The story
From Polybius + square (“grid”). It was invented by the Ancient Greek historian and scholar Polybius.
Etymology from Wiktionary, CC BY-SA 4.0.
Polybius square
Today it means: A character code represented by two sets of six lit torches, used to send messages character by character, in a two point visual fire telegraph. The character code is generated by encoding characters in a grid, where each character generates two numbers, uniquely representing each character as a pair of numbers. Full definition →