Serverless as 3) An application which run on a network and communicate with others on an equal status, you cannot distinguish one node from the others based on the source code or the logic it is running. In a sense even amazon serverless platform is not server less but it is server lite.
.. which have client and server parts of the protocol, that can be separately disabled. The fact that same piece of software can run on in client mode and in server mode is irrelevant.
In bittorrent example, the seeders are pure servers, and those cheating aps which only connect to seeds are pure clients. Yes, many trackers actively try to detect and discourage pure clients, but this is not enforced by the protocol itself.
1) An application which runs on a network and services clients 2) A dedicated computer which runs server applications.