Vega
Vega is the sensitivity of option value to implied volatility — the vol-dollar you are long or short.
Definition
Vega refers to the vol-dollar you are long or short. Keep that definition fixed when comparing series, managers, or regimes — renaming the same tape does not create a new signal.
Why it matters
Options and futures embed views on vol, skew, and path that cash markets only hint at. When the vol-dollar you are long or short shifts, related hedges, limits, and narratives usually need an explicit update rather than a quiet assumption.
Case
Suppose a desk is positioned for the opposite of what vega is saying. If the vol-dollar you are long or short moves against that book, the first question is not “is the story clever?” but whether size, hedges, and stop logic still match the observation.
How to read it
State the expiry and Greek exposure; unmarked vol or pinning effects rewrite the thesis. Prefer a short written null hypothesis for Vega: what would falsify the current reading in the next window?