Define the Programmable logic devices (PLD)?

In the world of digital electronic systems there are three essential kinds of devices 1.memory, 2.microprocessors, and 3.logic. The Memory devices store random information such as the contents of a spreadsheet or database. The Microprocessors execute software instructions to perform a wide variety of tasks such as running a word processing program or video game. The Logic devices provide specific functions, including device-to-device interfacing, data communication, signal processing, data display, timing and control operations, and almost every other function a system must perform.