If something is packaged, it's inside a box, bag, or other container. While packaged foods usually last longer, they're sometimes not as healthful as fresh, unprocessed food.
Anything inside a package can be described as packaged, from packaged lunch meats to your brand new packaged T-shirts that just arrived in the mail. You can also use this adjective to mean "attractively presented," like the perfectly packaged life your best friend posts on social media. Packaged comes from the Dutch pakkage, "baggage."