Many microchips these days are only available in a SMD (Surface Mount Device) packages. These chips have very tiny legs that are very close together making them super difficult to individually solder. The leg spacing and orientation also means that the chips can not be put in a breadboard for experimentation.
A breakout board is a basic printed circuit board PCB that has the surface mount chip soldered on and some or all of the pins connected to more easily accessible solder points or holes.
In addition the breakout board may include a few little passive components like resistors or capacitors to support the main microchip so you don't need to add them.
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