There are several ways to answer this question.
In general: vertical. Literally, 8″-9″ depending on use and jurisdiction.
For most publicly use spaces most designers will use a 7″ riser (vertical) and 11″ tread (horizontal) or 6″R and 12″T as the general layout with adjustments for the final heights and materials used.
For lower steps a portion is used based on a typical human stride of roughly 23″-24″.
Private stairs can go down to 9″R and 6″T, but this is typically uncomfortable to most people and would require use of handrails.
Stairs that have a rise higher than 9″ is called a ship ladder and require handrails along its length for additional support.
Vertical to near vertical systems would usually be called a ladder. Steps or rungs tend to be between 9″-12″ apart.
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