Goroutines are functions or methods that run concurrently with other functions or methods. Goroutines can be thought of as light weight threads. The cost of creating a Goroutine is tiny when compared to a thread.
You can observe that since we called `say("hello")` in a goroutine, it'll run concurrently and will print the output in no particular order in regards to the regualar function call `say("world")`.