Staircase glossary

US and UK usage both, because they differ and the difference matters.

Baluster: An upright between the handrail and the string or tread. Also called a spindle.
Balustrade: Handrail, balusters and newels together, as an assembly.
Blockings: Blocks fixed to a carriage to support the treads between strings.
Bracket: A decorative or supporting piece fixed to the face of a cut string beneath each tread.
Carriage: An intermediate raking bearer under a wide stair, between the two strings.
Closed string: A parallel-sided string with the treads and risers housed into it and wedged. Also called a housed string.
Cut string: A string cut to the profile of the steps, with the treads sitting on top of it.
Flight: An uninterrupted run of steps between two floors or landings.
Going: UK: the horizontal distance from one riser face to the next. The US equivalent is run, though US tread depth is measured nosing to nosing.
Guard: The barrier at an open edge of a stair or landing, preventing a fall. Includes but is more than the handrail.
Handrail: The rail the hand holds. Height is measured vertically from the pitch line.
Headroom: Clear height measured vertically from the pitch line to whatever is above. 80 inches under the IRC and IBC; 2000mm under UK Part K.
Landing: A level platform at the top, bottom or between flights.
Newel: The post at the foot, head and turns of a stair, anchoring the handrail and often the strings.
Nosing: The projection of a tread beyond the riser below it. IRC: ¾ to 1¼ inches. UK: maximum 25mm projection.
Open riser: A stair built without riser boards, leaving a gap between treads. Restricted or prohibited in some occupancies.
Pitch: The angle of the stair, measured from horizontal. Comfortable is 30 to 37 degrees; UK Part K caps a private stair at 42.
Pitch line: The notional line joining the tread nosings. Headroom, handrail height and string margin are all measured from it.
Rise: The vertical distance from the top of one tread to the top of the next. Total rise is finished floor to finished floor.
Riser: The vertical face between consecutive treads, or the board forming it.
Run: US: the horizontal distance covered by one step. Total run is the horizontal distance covered by the whole flight.
Step: Tread and riser taken together.
String / Stringer: The raking member at each side of a stair carrying the steps. String is the UK term, stringer the US one.
String capping: A moulding along the top of a closed string, often housing the balusters.
String margin: The distance from the top edge of a string to the pitch line, measured at 90 degrees to the pitch line.
Throat: The remaining depth of material behind a stringer cut. Too little and the stringer is a row of sawteeth.
Tread: The horizontal surface of a step, or the board forming it.
Walk line: The assumed path of travel across a tapered tread, where the going is measured. 12 inches from the narrow edge under the IRC.
Wall string: The string fixed flush against a wall.
Winder: A tapered tread, narrower at one end, used to turn a stair through 90 or 180 degrees without a landing.