What is this parenthesis enclosed variable declaration syntax in Go?

I am trying to find some information on parenthesis enclosed variable declaration syntax in Go but maybe I just do not know its name and that's why I cannot find it (just like with e.g. value and pointer receivers).

Namely I would like to know the rules behind this type of syntax:

package main

import (
    "path"
)

// What's this syntax ? Is it exported ? 
var (
    rootDir = path.Join(home(), ".coolconfig")
)

func main() {
  // whatever
}

Are those variables in var () block available in modules that import this one?