Its a self defined Function inside a Interface.
https://docs.unrealengine.com/latest/INT/Engine/Blueprints/UserGuide/Types/Interface/index.html
https://docs.unrealengine.com/latest/INT/Engine/Blueprints/UserGuide/Types/Interface/UsingInterfaces/index.html
Nothing Special and used pretty often.You should be able to find lots of ressources about Interfaces.