What is the use of flavorDimensions in builld.gradle (AndroidStudio)?

Question

I opened one project in build.gradle was also something unfamiliar to me:

flavorDimensions "release", "default"

productFlavors {

        main {
            applicationId "com.xxxx.xxxx"
            dimension "default"
        }
        underground {
            applicationId "com.xxxx.xxx"
            dimension "default"
        }
        google {
            dimension "release"
        }
        amazon {
            dimension "release"
        }
}

What is the use of this?