Microprocessor development board
A Microprocessor Development Board is a printed circuit board containing a microprocessor and the minimal support logic needed for an engineer to become aquinted with the microprocessor on the board, and to learn do some elementary assembler programming on it. It also servers for the producer of the microprocessor as a platform for testing their new chip.
It differs form a home computer by the lack of a Video Display Controller, and any other logic that is not needed just for testing a microprocessor, such as a sound-chip. The reason for the existence of the development board is in learning, not in entertainment. To keep cost down it normally came without an enclosure, or a power supply, because they were thought to be unneccesary, and because the board could be powered by a typical bench power supply.
Input was most often done with a hexadecimal keyboard, and the display mostly consisted of a 7-segment display. Backup storage of written assembler programs was primitive, only a cassette type interface was provided.
Often the board has some kind to expansion connector that brought out all the necessary CPU signals, so that an engineer could build and test an experimental interface or other electronic device.
Interfaces to the bare board were often limited to a RS232 serial port, so a terminal could be connected, or an interface for a printer or teletypewriter.
Although these development boards were not designed by hobbyists, they were often bought by them because they were the earliest devices you could buy. They often added all kinds of expansions, such as more memory, a video interface etc. Very popular was to use (or write) an implementation of Tiny Basic.