n. A pair of yellow lines that cars are not allowed to cross. Used for separating lanes of opposing traffic and creating borders around medians. Also used to prohibit entry and exit from high occupancy vehicle (carpool) lanes.
I got a ticket for crossing the double yellow when I turned left.
I had to go to my boss, then accounting, legal, back to accounting, back to my boss, to operations, legal, and back to my boss again on this project. I've been banging my head in circles all afternoon. <bang (one's) head in circles>