What is a microprocessor development board used for?

Microcontroller development boards, also called development kits, help the system designers to develop and test projects easily and speedily.

A single-board microcontroller is a microcontroller built onto a single printed circuit board. 

It's containing a microprocessor and the minimal support logic needed for an electronic engineer or any person that wants to become acquainted with the microprocessor on the board and to learn to program it.This board provides all of the circuitry necessary for a useful control task: a microprocessor, I/O circuits, a clock generator, RAM, stored program memory and any necessary support ICs.