The conjunction as has several different meanings. We use as when one event happens while another is in progress (‘during the time that’). In this case the verb after is often in the continuous form: They arrived as we were leaving. (time conjunction meaning ‘while’ or ‘when’)

Meaning of as in English as adverb us strong / æz / weak / əz / uk strong / æz / weak / əz / Add to word list A2 used in comparisons to refer to the degree of something: She'll soon be as tall as her mother.

Grammar > Adjectives and adverbs > Adjectives > Comparative and superlative adjectives > As … as from English Grammar Today We use as + adjective/adverb + as to make comparisons when the things we are comparing are equal in some way: The world’s biggest bull is as big as a small elephant. The weather this summer is as bad as last year.