Runtime Identifier (RID) values are used to identify target platforms where an application will run. They're used by .NET packages to represent platform-specific assets in NuGet packages.
From the .NET Core Runtime Identifier (RID) Catalog:
Runtime Identifier (RID) values are used to identify target platforms where an application will run. They're used by .NET packages to represent platform-specific assets in NuGet packages. The following values are examples of RIDs:
linux-x64
,ubuntu.14.04-x64
,win7-x64
, orosx.10.12-x64
.RIDs that represent concrete operating systems usually follow this pattern:
[os].[version]-[architecture]-[additional qualifiers]
.