const declares a constant value.

A const statement can appear anywhere a var statement can. Constant expression perform arithmetic with arbitrary precision. A numeric constant has no type until it's given one, such as by an explicit conversion.

A number can be given a type by using it in a context that requires one, such as a variable assignment or function call.

package main

import (
  "fmt"
  "math"
)

const s string = "constant"

func main() {
  fmt.Println(s) // constant

  const n = 500000000

  const d = 3e20 / n
  fmt.Println(d) //6e+11
  fmt.Println(int64(d)) //600000000000
  fmt.Println(math.Sin(n)) // -0.28470407323754404
}