Built-ins mean something that is integrated into any structure or object. This also has some other dimensions in terms of its meaning.
Built-ins make up a vital component of any object, structure, or item that is often constructed/built as a recess in something for some cases. This means something built into something, i.e. like an in-built swimming pool, for instance. It also means something which is integrated. It means something built as a part of a bigger unit and is not usually detachable, like a built-in wardrobe or cabinet for instance. It also means any crucial or permanent quality, attribute, or element.
Built-ins are aspects/items which are attached to any property on a permanent basis and these include items like cabinets, wardrobes, appliances, and more. Built-ins are items which are always parts of properties and their permanent structures. These include appliances, furniture, cabinetry, and a lot more. Built-ins are specified in any sale or lease transaction or deed. This could be an aspect of negotiation amongst buyers, sellers, developers, or agents.