Enum downloadStatus switch statement

Im confused as to what the (let failure) Is doing.

enum Status { case Success case Failure(String) }

let downloadStatus = Status.Success

switch downloadStatus { case .Success: println("The download was successful") case .Failure(let failure): println(failure) }

You have associated a string with the Status member Failure. So in the switch statement why are we creating a constant called failure with a lower case?

Wouldn't we create a string like "Download unsuccessful "

Or are we passing a constant in the switch statement and assigning our string to the constant failure? Just seems pretty confusing now we have enum Status member Failure and our constant for its string lowercase failure