"A power take-off or power takeoff (PTO) is a term for methods of taking power from an operating power source, such as a running engine, which can be used to provide power to attachments or separate machines." http://en.wikipedia.org/wiki/Power_take-off
"A microcontroller (sometimes abbreviated µC, uC or MCU) is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. " http://en.wikipedia.org/wiki/Microcontroller
In other words, it's a small/cheap computer that you can use for a specific function like monitoring the temperature of your greenhouse and sending you a text message when it gets too hot.