It's much simpler than that. It's just a way of defining cleanup functions without having a language-level concept of destructors. Here's an example: https://gobyexample.com/defer.

This simple example should explain everything:

    package main

    import "fmt"

    func function1() {
        defer fmt.Println("function1: defer a")
        fmt.Println("function1: inside")
        defer fmt.Println("function1: defer b")
    }

    func main() {
        fmt.Println("main: before function1")
        function1()
        fmt.Println("main: after function1")
    }

Here is the output:

    main: before function1
    function1: inside
    function1: defer b
    function1: defer a
    main: after function1

All defers run in LIFO order at the point when a function returns before the function returns execution back to the caller.