Sofema Online (SOL) www.sofemaonline.com considers the typical terms and abbreviations compliant with ICAO Document 9640 and SAE AS6285E
Abbreviations and Terms
Active frost: Condition when frost is forming. Active frost occurs when
(1) the aircraft surface temperature is at or below the frost point, or
(2) there is water in liquid form (e.g., dew) on the aircraft surface and the surface falls to/or below 0 °C (frozen dew).