A power-on self-test (POST) is a diagnostic process that runs when a server is turned on to check the basic functionality of the hardware components and report any errors or faults. A POST code is a series of beeps or flashes that indicate the status of the POST process and identify any problems that prevent the server from booting up. A POST code can be heard through a speaker or seen on a display attached to the server motherboard. A POST code is useful for diagnosing errors without opening the machine or using any software tools. References: CompTIA Server+ SK0-005 Certification Study Guide, Chapter 5, Lesson 5.1, Objective 5.1