The story
From the mathematical formula (∂𝒱)/(∂σ), the partial derivative of vega (𝒱) with respect to volatility (σ), pronounced as "D vega (by) D vol(atility)".
Etymology from Wiktionary, CC BY-SA 4.0.
DvegaDvol
Today it means: A second-order measure of derivative price sensitivity, expressed as the rate of change of vega with respect to changes in the volatility of the underlying asset. Full definition →