What is the purpose of "imports" in project.json of .NET Core apps?

imports-in-project.json

{
	"version": "1.0.0-*",
	"testRunner": "xunit",

	"dependencies": {
		"Microsoft.NETCore.App": {
			"type": "platform",
			"version": "1.0.0"
		},
		"xunit": "2.1.0",
		"dotnet-test-xunit": "1.0.0-*",
		"Moq": "4.6.36-alpha",
	},

	"frameworks": {
		"netcoreapp1.0": {
			"imports": [
				"dnxcore50",
				"portable-net45+win8"
			]
		}
	}
}