.NET Core is an open-source, general-purpose development platform
maintained by Microsoft and the .NET community on GitHub.
It's cross-platform (supporting Windows, macOS, and Linux)
and can be used to build device, cloud, and IoT applications.

This package contains everything you need to run a ASP.NET application. 
It includes ASP.NET Core runtime and .NET Core runtime.
If you want to build apps, install .NET Core SDK (dotnet-sdk), which contais these runtimes too.