FF&E (often pronounced "F-F-and-E") is industry shorthand for everything you'd take with you if you moved out: sofas, beds, dining chairs, lighting fixtures (when they're not hardwired), rugs, art, accessories, appliances. It's contrasted with the building's "shell" or "fixed" elements — walls, floors, plumbing, hardwired lighting, built-in cabinetry.
The distinction matters because FF&E is where most of the visible style and personality of a space lives, and where most of the budget often goes (a high-end sofa alone can cost what an entire kitchen renovation does). It's also where the most decisions get made — there are far more sofas in the world than there are wall-paint colors.
Designers track FF&E in spreadsheets — every item with vendor, SKU, cost, lead time, and status. For a single-room redesign, an FF&E list might be 15 items; for a full home, it can be 200. The list is what turns "the design concept" into "actually delivering the project".