The upright member of a step situated at the back of a lower tread and near the leading edge of the next higher tread.
Merriam-Webster Online Dictionary
riser (noun)1.
one that (as from sleep) - rises
2.
the upright member between two stair treads
3.
a stage platform on which performers are placed for greater visibility
4.
a vertical pipe (as for water or gas) or a vertical portion of an electric wiring system
5.
one of the straps that connects a parachutist's harness with the shroud lines
Elevation, Booster, Enhancer, Uplifter, Stimulator