Environment in which a piece of JS is executed. Stores all the necessary information for some code to be executed. Exactly one global execution contex
callback : ๋น๋๊ธฐ ์ฒ๋ฆฌ์ ์์๋น๋๊ธฐ ํ๋ก๊ทธ๋จ 1. callback 2. promise 3. async awaitJavaScript is synchronous.(๋๊ธฐ์ ์ด๋ค. ๋๊ธฐ์ => ์ ํด์ง ์์์ ๋ง๊ฒ ์คํ๋๋ ๊ฒ)Execute the code block i