'Unpack' means to take things out of a package or temporary storage like a luggage bag. Usually to put them in their proper place. This phrase often is used in relation to personal problems people are discussing, often as a subtle way to indicate there's baggage involved in the conversation or issue that needs to be broken down and evaluated.

The phrase can be used when there is a lot of information to process or problems to solve. It's a response provided by a person asking the other to slow down and give time to sort out what they've been given.
"Okay Angel, you just gave an hour-long monologue about how your girlfriend dumped you because you can't hold a job to pay your car loan, your mommy issues, getting fired, and your confusion which pronoun you want to be called. There's a lot to unpack here."

"Look Karen, you can't just hand me a 30-page document that I've never seen, then demand I give you an answer why it's messed up. Especially when you expect the answer in less than three minutes. There's a lot to unpack here."

"Whoa, whoa, whoa! There's a lot to unpack here!"
by Johnny Atkins November 21, 2019
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