When it comes to implementing distributed systems, there are a whole variety of consistency models to choose from. Going through papers on system implementations of varying degrees of consistency guarantees (e.g.Spanner or Bayou), I found myself mixing up strictly different terms and models. To prevent further confusion, I thought it would be a good idea to cover some key terminologies here. What is Consistency? There are myriads of different consistency guarantees, but what is consistency in the context of distributed systems in the first place?