Correction
The 10% figure is the convention that separates a correction from ordinary day-to-day noise, and the 20% ceiling separates it from a full bear market. Think of corrections as the middle tier of a three-level scale: normal pullback (under 10%), correction (10–19.9%), and bear market (20% or more). The boundaries are widely used but not set by any official body — they are simply the market's common language.
Corrections are measured from the most recent closing high. Suppose an index closes at a peak of 10,000 points (hypothetical), then falls to 8,900 — that is an 11% decline and qualifies as a correction. If it rebounds before hitting 8,000, it never becomes a bear market. This matters because percent-change columns on a data platform show exactly where an index stands relative to its recent high, letting readers identify which tier applies.
A common source of confusion is timing. Corrections can happen very quickly — sometimes within days — which makes them feel more alarming than the numbers might suggest. They can occur inside a longer bull market without ending it. Economists read corrections as normal price-discovery events; they become noteworthy mainly when they deepen or when market breadth (the share of stocks falling) is unusually wide. See also how to read percentage moves for context on interpreting these figures.