Gridlock is traffic so blocked that nothing can move at all. Total gridlock, gridlock in the city centre, political gridlock.
The word describes a specific failure: cars stopped in a junction block the crossing traffic, which then blocks the next junction, until a whole grid is locked and no movement anywhere can free it. Political gridlock borrows exactly that image.
1noungridlockTraffic so blocked that nothing can move at all.
“An accident on the bridge caused gridlock across the whole city centre.”
gridlock is a blockage.
Grid plus lock, coined in New York in the 1970s for exactly this failure of a street grid.
From grid + lock.
Etymology from Wiktionary, CC BY-SA