The conformational preference of an equatorial compared to an axial substituent in a monosubstituted cyclohexane. This steric substituent parameter equals ΔrG° in kcal mol-1 for the equatorial to axial equilibration on cyclohexane. The values are also known as 'Winstein–Holness' A values.
Source:
PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1087 (https://doi.org/10.1351/pac199466051077)