A sailplane is normally regarded as having a good performance in soaring with an excellent glide angle.
'Glider' is an overall term and covers sailplanes and the army gliders used, for example, in WW2. Gliders now include the old air cadet gliders like the Slingsby T21b - I own a share in one of those and fly it regularly in Summer, but not in Winter as it has an open cockpit.
I never think there is a hard & fast rule, but my Ka6 is definitely a sailplane as far as I'm concerned. It flies so beautifully as well with excellent flight handling and good soaring performance. Not as good as the modern glass fibre aircraft, but still nice to fly. The old wooden sailplanes have a sort-of charm about them - a bit like classic cars really. I like to park my 1964 Mini next to my 1965 Ka6 on the airfield. It's a bit like yachts & boats. A yacht is always a boat, but a boat is not necessarily a yacht.
Gliding is a lot less expensive than classic car ownership and maintenance. My aircraft cost me £2000 inc. trailer, 'chute and rigging gear.
Edited by Cooperman, 23 January 2015 - 07:48 PM.