A riser is the vertical part of a staircase step, the board or surface that connects one step to the next. When you climb stairs, your toes might brush against the riser as you lift your foot to the next level. The flat part you actually step on is called the tread, while the riser fills the space between treads.

Some staircases have open risers, meaning you can see through the gaps between steps. Others have closed risers, which make the staircase feel more solid and finished. Architects pay attention to riser height because if risers are too tall, stairs become exhausting to climb; if they're too short, you might trip because your natural stride doesn't match the steps.

The word can also describe someone who gets out of bed at a particular time. An early riser wakes up with the sun, while a late riser prefers sleeping in. If you naturally wake up at 6:00 a.m. full of energy, you're an early riser. If your parents have to call your name three times before you finally drag yourself out of bed at 9:00 a.m. on weekends, you're definitely a late riser.