Turnkey refers to something that is ready for immediate use, generally used in the sale or supply of goods or services. Turnkey is often used to describe a home built on the developer's land with the developer's financing ready for the customer to move in. If a contractor builds a "turnkey home" they frame the structure and finish the interior. Everything is completed down to the cabinets and carpet. "Turnkey" is commonly used in the construction industry, for instance, in which it refers to the bundling of materials and labor by sub-contractors. 'Turnkey' is also commonly used in motorsports to describe a car being sold with drivetrain (engine, transmission, etc.) to contrast with a vehicle sold without one so that other components may be re-used.
The term turnkey is also often used in the technology industry, most commonly to describe pre-built computer "packages" in which everything needed to perform a certain type of task (e.g. audio editing) is put together by the supplier and sold as a bundle. This often includes a computer with pre-installed software, various types of hardware, and accessories. Such packages are commonly called appliances. A website with a ready-made solutions and some configurations is called a turnkey website.
Turnkey products are synonymous to "off-the-shelf" solutions and not customized.