The Raspberry Pi is a credit-card sized computer that plugs into your TV and a keyboard. There have been several generations of the device with improved performance, more memory, and more connectivity. This tag should be used for electrical engineering questions that involve the use of a Raspberry Pi. For questions about the Raspberry Pi itself see the raspberrypi.stackexchange.com Raspberry Pi specific forum.
The Raspberry Pi is a single-board computer developed in the UK by the Raspberry Pi Foundation. The Raspberry Pi is a credit-card sized computer that plugs into your TV and a keyboard.
It’s a capable little PC which can be used for many of the things that a desktop PC does, like spreadsheets, word-processing and games. It also plays high-definition video.
There are several generations of the Raspberry Pi as well as several variants. More recent generations such as the Raspberry Pi 3 have faster processors and more capabilities such as WiFi and Bluetooth.
The processor used depends on the Pi generation though all as of 2017 are ARM processors. The design does not include a built-in hard disk or solid-state drive, instead relying on an SD card for booting and long-term storage. A self powered drive connected through USB for large amounts of storage can also be used.
The standard operating system is Raspbian, a version of Linux, however other operating systems are available on later generations of Pi due to the improved performance of the processor being used with more recent versions.
Note that SE has a Raspberry Pi site.