We called them a Guard'svan and Van down here since that is where the Guard of the train rode, usually on the rear not always: the only Brake Vans were used on the Centre-rail inclines such as the Rimutaka Incline and the few steep West Coast branchlines that also had the Fell centre rail for braking. Van's came off our trains in 1986 except those on passenger trains. The Guard's duties were given to the Loco Assistant aka fireman and called a Train Operator.
Brake van was a British term since they didn't go in for brakes on goods train and had little in the way of hills, I've heard Canadians refer to them also as a Van.
See my thread [
ngdiscussion.net] top 3 photos for the Brake Van.