A slang word for cumbersome, awkward and unnecessarily outdated when there's usually a more sleek and functional alternative thanks to modern technology. Carrying a bunch of luggage to a car strapped to your back would be clunky compared to just using an dolly, or perhaps an anti-gravity device if only those things had been invented yet. You get the idea. Clumsy in form or manner; awkward.

There are some fashions with are considered clunky, like bell bottoms for pants, or platform shoes from the disco period. God, it's hard to believe people used to dance in those things.