Definition
A small character, number, or symbol written below the normal line of text, typically used in technical and scientific notation to identify a specific variable, condition, or component within a formula or expression.
Plain English
A small letter or number sitting below the main line of writing, used to label or distinguish one item from another in a formula.
Context Anchor
Seen in aircraft manuals, performance charts, and technical formulas where small letters or numbers are attached to symbols.
Derivation
From Latin sub- meaning 'under' and scriptum meaning 'written.' Literally 'written under' — which is exactly what a subscript is: a character written below the line.
Why Pilots Care
Correct reading of subscripts prevents confusion between related but distinct values like stall speed versus approach speed.
Intuition Check
Do not read a subscript as a separate number to add or as decoration. It is part of the symbol and helps identify the exact meaning.
Example Sentence 1
In the formula for density altitude, the subscript on each pressure value tells you which altitude that pressure refers to.
Example Sentence 2
In the takeoff distance chart, the V1 subscript showed the decision speed for the current weight.