The Big Processor Guide - Cores Introduction
"Core" is a term that takes a lot of abuse.
But for the purposes of this guide, a "core" is a processor design. This essentially means dividing up all the processors under discussion based on the codenames given to them by their manufacturers. In this way, "core" becomes something of a shorthand for "codename".
This is a more carefully constructed definition than you might expect. Partially, this is to avoid ambiguity about how different two chips have to be in order to be thought of as different cores. Sometimes two chips of the same core may differ a fair amount, and sometimes two chips of different cores may be virtually identical.
Codenames make a convenient way to classify processors, because they are usually unique identifiers, they're memorable, and in practice the codename for a processor is the best way to distinguish it from others. While there are certainly flaws in this approach (notably, when the lines between cores get blurred), it is a common and reasonably reliable scheme.
This subsection of the guide dissects the different processors under study, splitting them based on both their official product names and their internal codenames.