A stair is one of a series of steps that lets you move between different levels of a building. When you climb stairs at school or home, each individual step you place your foot on is a stair. The whole connected set is called a staircase or stairway, but each single step is a stair.

Stairs are one of humanity's oldest and most practical inventions. Ancient civilizations built grand staircases into pyramids and temples. Medieval castles had narrow, winding stairs that defenders could protect easily. Today, stairs range from the plain concrete steps in a parking garage to the elegant marble staircases in museums and government buildings.

The word appears in several common expressions. When someone takes things one step at a time, they're tackling a big challenge bit by bit instead of trying to leap to the top all at once. Something described as a stair-step pattern rises in distinct levels, like stairs going up.

People sometimes confuse stair with stare (to look intently at something), but they're completely different words that just happen to sound alike.