East Asia
The Orient
noun
East Asia is East Asia, otherwise known historically as the Orient.
東亜 is an older way to say "East Asia," covering countries like Japan, China, and Korea. These days, people usually say 東アジア instead, but you'll still sometimes see 東亜 in old writing and as part of proper nouns.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
太平洋戦争のことを、大東亜戦争と呼ぶのは何故ですか。
Why is the Pacific War called The Greater East Asian War?