https://writings.quilt.org/2014/05/12/distributed-systems-and-the-end-of-the-api/
"A distributed system is one where a machine I've never heard of can cause my program to fail" - Leslie Lamport
Cute, but "my program" is kind of quaint now, isn't it?
"...multiple processes that must communicate to perform work" - hmm, hmm, let me tell you about disk controllers. Oh wait, that's your point... almost, "an air-gapped computer" is considered nondistributed, but well whatever.