Definition
Two parallel runways at the same airport whose thresholds are not aligned with each other but are staggered, so one runway's landing threshold is displaced ahead of or behind the other's along the direction of flight.
Plain English
Two runways that run in the same direction side by side, but the start of one runway is set forward or back compared to the start of the other.
Context Anchor
Seen on airport diagrams, in runway planning, and when comparing closely spaced runways at larger airports.
Derivation
Offset' means shifted out of alignment. 'Parallel' means running in the same direction without meeting. Together they describe two same-direction runways whose start points are shifted relative to each other.
Why Pilots Care
The offset determines whether simultaneous operations are permitted and changes the required separation between aircraft on adjacent runways.
Analogy
Think of two pencils lying in the same direction on a desk, but one pencil is slid forward compared with the other. They are still parallel, but they are offset.
Intuition Check
Offset does not mean the runways cross or point in different directions. They remain parallel; they are simply staggered along their length.
Example Sentence 1
Because the airport has offset parallel runways, the threshold of Runway 27L sits about a thousand feet ahead of Runway 27R.
Example Sentence 2
Because the runways are offset, the tower can launch a departure from one while an arrival is still on short final to the other.