The term &quot;protocol&quot; is held over from Obj-C. I guess because in Obj-C, the declaration of a class is wrapped in @interface...@end (the implementation is inside @implementation...@end)<p>And it&#x27;s annoying to have to explain this to all the other devs on the team who don&#x27;t use Obj-C. Here&#x27;s hoping Swift fixes the vocabulary.<p>EDIT: I suppose the main difference between Swift&#x27;s &quot;protocol&quot; and Java&#x27;s &quot;interface&quot; is that Swift lets the dev provide actual implementations for some declared functions. &quot;Protocol&quot; is still not an idea word in my opinion.