(something happens) as (something else happens)

Talk about two ongoing things happening at the same time with "as":

The sky started to get darker as we were walking.

I like to listen to audio-books as I'm driving.

"As" can also come at the beginning of a sentence without changing the meaning:

As we were walking, the sky started to get darker.

"As" is similar to "while". But you can also use "while" when one event was ongoing but the other event wasn't:

Someone called while I was taking a shower.

"As" would not fit perfectly in that sentence, but it wouldn't be completely wrong. So it's safe to think of "while" and "as" as being the same.

This phrase appears in these lessons: