Microsoft has never been understandable. I tried to find an overview of dot net on their site, when dot net was at 1.x and was going to cure world hunger, but I wasn't able to understand what they meant by the '.net platform'. Gave up after an hour.

.net been many things over the years and included many things. I guess if there was a definition at it's core (no pun intended) it's a managed code runtime with an associated set of libraries and framework to develop applications. But it's also a brand name for Microsoft development tools and frameworks. But it's very much not precise in how it's used by MS itself.