Wingspan: In birds (Aves) - "the distance between the wing tips when the wings are held outstretched" (Wikipedia) or "wingtip to wingtip in flight" (BTO).
In winged insects (Insecta) - "may refer to the distance between the centre of the thorax to the apex of the wing doubled or to the width between the apices with the wings set with the trailing wing edge perpendicular to the body" (Wikipedia)
Note: For wingspan you can specify the measurement type (minimum, maximum, average), gender (male, female) and life stage.
Definition requires specialist input.
This definition requires amendment by the relevant taxonomic experts.