"What is a weather delay?"

A weather delay is when adverse weather can or is affecting the ontime departure of a flight. It is vague as there are many reasons for a weather delay.
-weather at origin
-weather at destination
-weather enroute
-forecasted weather
-deicing
-late inbound aircraft as a result of a weather delay at another station
-late crew/passengers due to off scheduled operations due to weather delays
-ATC delays due to weather
-terminal constraints due to weather
etc etc etc