Dynamic_Runtime
dynamic
Keyword as dynamic added to give more context Swift runtime to use Objective-C dynamic dispatch. Mostly used Key Value observing.
@objc
Very less experience in these scenarios.
@objc could be also tacked on to give access for Objective-C caller.
Method swizzling via Objective-C could be a scenario if it comes to my mind or Objective-C library dependencies - interoperability with swift.
#selector kind of thing.
Another term is called monkey patching