How much a premium changes for a one-point move in the index. A call's runs from near zero to near one and a put's from zero to minus one, with about a half at the money. Traders also read it as rough shorthand for the chance a contract ends in the money; the two are close but they are not the same quantity.
Mayawhat these words mean
Maya reads the desk’s written explainers and the glossary. She holds no market data at all, so she can say what a thing is and cannot say what it is doing today.