closure is a function inside another function where you can reference variable defined in the outer function. I have seen them useful in dealing with packages where a function expects an type func() as an argument where the func() doesn’t take any argument. example from package github.com/cenkalti/backoff signature of backoff.Retry is as below backoff.Retry(o backoff.Operation, b backoff.Backoff) where backoff.Operation is of type func() error type Operation func() error func main() { func retryWrapper(imp string) func() error{ return func() { funcThatCouldFail(imp) retun nil } } err := backoff.