Net Core, Net Framework, Net Common Core, .NET..
And God forbid any of these frameworks ever expose what they are in a config file. You start a project, hand it to a colleague and he can't figure out whether it's Framework or Core by looking at the files. You Google and are immediately bombarded by 15 year old threads.
And the .csproj files do tell you which .NET they are.
<TargetFrameworkVersion>v4.</TargetFrameworkVersion> or <TargetFramework>net4</TargetFramework> is the old framework. Also, if the file is an unreadable mess listing all .cs files, it's generally .NET Framework.
<TargetFramework>netstandard2.0</TargetFramework> is .NET Standard 2.0, which means this library can be consumed from either Framework or modern .NET.
And finally, <TargetFramework>netX.0</TargetFramework> (X >= 5) is the modern .NET.