The Brief: For days means "in abundance".
For days is an idiomatic expression used to describe a conspicuous abundance of a certain trait, feature, or item. The idea is that someone posesses so much of something that it seems to last “for days.”
The phrase is a synonym for all the.
— DestinationCleveland (@TheCLE) February 28, 2019
Ears for days pic.twitter.com/Wv6gM20OxZ
— Kage (@Kagewuffs) February 28, 2019
Legs for days
A common usage is “legs for days.” This particular iteration typically describes a woman with long, attractive legs.
Legs for days 💅🏼 pic.twitter.com/UKTUzAfwoA
— Sweet🍬 (@_ncsweet) February 25, 2019