javascript - What is the difference between "let" and "var"?

ECMAScript 6 introduced the let statement.
I've heard that it's described as a local variable, but I'm still not quite sure how it behaves differently than the var keyword.
What are the differences? When should let be used instead of var?
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hoisted but not initialized: stackoverflow.com/questions/31219420/are-variables…
the temporal dead zone: stackoverflow.com/questions/33198849/what-is-the-t…