the.com/sleeve notes

means The printed commentary tucked inside or on the back of a record sleeve, explaining the music, crediting the musicians, or offering context you may or may not have wanted.

from Straightforward compound: 'sleeve,' the paper or cardboard jacket protecting a vinyl record (itself borrowed from the garment sense, something that slips over and covers), plus 'notes' in the sense of written remarks. As vinyl albums became a serious medium in the mid-20th century, record labels started printing essays, credits, and lyrics on or inside the sleeve — partly information, partly marketing, partly a place for critics and producers to flex. The term stuck even as formats changed; CD booklets and streaming 'liner notes' are the same impulse wearing a new jacket.