ris ‧ er /ˈraɪzə $ -ər/ BrE AmE noun [countable]
1 . early/late riser someone who usually gets out of bed very early or very late
2 . technical the upright part of a step on a set of stairs
3 . risers [plural] American English a set of wooden or metal steps that can be moved from place to place, used for a group of people to stand on:
The school choir stood on risers behind the orchestra.