They used to choose very bad names like .NET or COM [1] (this predates Internet) makes searching information very tricky. MSDN doesn't help.
Our internal libraries need to be compatible with the Core Runtime, so we have to have them target .NET Standard, which is compatible w/ the full .NET Framework or .NET Core. To target .NET Standard, you need the .NET Core SDK/CLI which includes the `dotnet` tool, which is almost never clarified as "the SDK/CLI" in documentation or in talks, but usually just ".NET Core".
Another minor annoyance: to build a .NET Standard-compatible library, you reference the "NETStandardLibrary" NuGet package. Makes a fair amount of sense, but is hard to talk about.
If you're running on Windows and want a smaller server footprint, you can use Windows Server Nano, which requires your apps to target .NET Core Runtime (not .NET Full Framework). Note that this requirement is not true for Windows Server Core. -_-
I later found out I could have looked for "ActiveX" and found similar results.
They have a product in Azure named simply DocumentDB. I don't think "used to" is necessarily the best tense here (:
What could you possibly mean by that? The .com TLD was introduced in 1985, with microsoft.com registered already in 1991. Microsoft COM was created in 1993. (Of course, "the Internet" in any sense of the word predates all of this.)