Subriser - Stairway Construction
A sub riser would be any riser that is underneath a finished riser. A good example of this would be the illustration below. The black arrow is pointing to a riser that was used to construct the original staircase, but another one will be installed over it as part of the finished stairway.
With proper planning, you could probably eliminate sub risers and treads. This might not be possible for every stairway, but if you're going to use 3/4" or thicker lumber, it might be.
Stairs / Stair Glossary
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z