The Slim is essentially a standard Softail (ie a big twin with hidden rear shocks for that ‘hardtail’ look) but given (as seems to be repeatedly fashionable with cruisers from all manufacturers at the moment) the minimalist, ‘50s ‘bobber’/hot rod look. The difference here, though, is the ‘Slim’ bit. Harley’s view was that its existing Softails had become ever bigger and plusher, the result being that the engine ended up looking smaller and smaller. With the Slim, the idea is to reverse that trend by making the bike slimmer at the rear so the engine looks larger in the frame, thus achieving more of a hot rod style.
It works, too, as was strikingly evident when following a Slim alongside a Fat Boy and noting starkly how clunky, fat and, yes, crude, the long favourite Fat Boy seemed by comparison.