Picture a city centre laid out in squares, like a grid. Cars roll forward into the junctions before there is room to leave them, and now every line of traffic is standing in another line's way. The light turns green and still nobody moves, because the way out is filled by people who are also waiting. Nothing is broken and nobody is driving slowly: the parts are simply into each other, and the jam cannot undo itself. That is the picture the word carries, and it carries the whole of it into a room full of arguing people, where each side is blocking the other and no one will back up first.
From the word’s history
The word is grid plus lock. Grid is the square pattern of city streets, and lock is what the traffic does to it.
這個字由 grid（城市棋盤格狀的街道）加上 lock（鎖住）組成，字面就是「整片格子被鎖起來」，跟現在的用法完全對得上。
Wiktionary entry for gridlock, kaikki source_ref 3f6f69a190036ae4:1238801529 — 'From grid + lock.'
登入就可以看每一支怎麼連回核心畫面。