about URL

use - or _ in the URL?

both - and _ are more readable than space, because space will encode to %20.
but it’s prefer to use - in the URL.
for example, we have pamameters keyword hello world, we can use hello-world or hello_world in the URL.
but in the google search, hello_world is same to helloworld, hello-world is same to hello world, the search result is different.
two keywords hello and world is what we want. so it’s prefer to use - in the URL.