Go: What is select in Go?

1select {
2case msg1 := <-ch1:
3    fmt.Println("Received from ch1:", msg1)
4case msg2 := <-ch2:
5    fmt.Println("Received from ch2:", msg2)
6case ch3 <- 42:
7    fmt.Println("Sent to ch3")
8case <-time.After(5 * time.Second):
9    fmt.Println("Timeout")
10default:
11    fmt.Println("No communication")
12}