Any event within the operational envelope of the airport, which has a significant negative impact on operational performance unless appropriate actions are organised.
SESAR Operational Service and Environment Definition (OSED) P.6.6.1, Ed.00.00.03, 20.01.2012
This definition encompasses adverse weather conditions.
In most cases, the airport capacity will be affected. However, other Key Performance Areas may also be impacted (e.g. the predictability of operations may decrease). The consequence of adverse conditions at an airport may be arrival and departure delays and / or flight cancellations. In many cases, the ATM Network will also suffer from the disruption. (same source)
Lexicon Release 2015.2