What are some popular English idioms and phrases?

Some popular (and potentially confusing) English idioms and phrases are "burning the midnight oil," "barking up the wrong tree," and "at the drop of a hat." "Burning the midnight oil" means working late, and alludes to a time when people worked by the light of oil lamps after dark.

"Barking up the wrong tree" means looking in the wrong place. Picture a dog barking at a squirrel in one tree after it has escaped into another. Doing something at the drop of a hat means doing it immediately. The idiom is a playful exaggeration that conjures up the image of something happening quickly, in the time it would take for a dropped hat to hit the ground.