Procedures

If you’re particular about names:

• The name “function” often implies zero side-effects. Just compute and return a value based on any args passed in, regardless of the state of any global variables. And no modifying any global variable either.
• The name “subroutine” often implies all side-effects, possibly accounting for values of globals, modifying globals, and may or may not return a value.

“Procedure” in a general term that covers both, and that’s what Odin uses. Ex.:

package my_pkg

import "core:fmt"

main :: proc() {
    n, m := 2, 3
    ans := foo(n, m)
    fmt.println(ans)
}

foo :: proc(num_1: int, num_2: int) -> int {
    return num_1 + num_2
}