As is a preposition or a conjunction. … As as a preposition We use as with a noun to refer to the role or purpose of a person or thing: … As as a conjunction The conjunction as has several different meanings. We use as when one event happens while another is in progress (‘during the time that’).

from English Grammar Today As is a preposition or a conjunction. As as a preposition We use as with a noun to refer to the role or purpose of a person or thing:

1: 'As' can mean 'because'. As it was raining, we stayed at home. 2: 'As' can mean 'while' or 'at the same time': As I was walking down the street, I saw Julie. 3: We can use 'as' to talk about the way one thing is similar to another thing.