What is the meaning of the word "turnkey"?

Definitions:

  1. a complete product that is ready to be deployed immediately, without further customization copy to clipboard noun
    • The new software package is a turnkey, so it only took a short time to install. copy to clipboard
  2. involving a complete product that is ready to be deployed immediately, without further customization copy to clipboard adjective
    • We don't have the resources to build up a custom system, so we went with a turnkey solution. copy to clipboard
  3. someone who guards prisoners copy to clipboard noun
    • One prisoner escaped by bribing the turnkey. copy to clipboard