RPi = Raspberry Pi!
It's an awesome little computer, a bit larger than a credit card, with all sorts of projects out there.
I personally have 3 RPis running my DIY bartop arcade cabinet, as a streamer running Kodi for the bedroom, and as an audiophile streamer from my HT Tower to my 2 channel rig in my man cave.
Another great project I've been considering is as a weather station and garden monitor. And, you can also run it as a wireless server for your 3D printer, and use the RPi camera to remotely monitor your 3D prints via WiFi!
https://www.amazon.com/CanaKit-Rasp...qid=1482769340&sr=1-2&keywords=raspberry+pi+3
It is not plug and play for any of these types of projects! Typically, you will have to image the sd card, and likely you will have to do some configs via command lines! But, YouTube is your friend.