An Arduino is a small device that allows anyone who know how to program it create what they can dream up. It allows information to move back and forth from a variety of sensors. Some call it physical computing but what that really means is the arduino and take information from the world around it and interact with it.
Some devices, like the Arduino and the Raspberry Pi, need instructions to function. Coding is when someone adds or uploads instructions to the device.
The term Hacking once had a very negative meaning. Nowadays, hacking is taking something you own and changing it to suit your needs. Some have referred to it as "voiding the warranty". Occasionally, a hack results in an improvement in the product/item.
When someone refers to a device or software being open source, they are referring to it being free to change and modify. Usually, the reference is used for software, meaning that anyone can add and improve the software without fear of consequence from the original programmer.
Creating a product or service new and unique from hardware or the use of software to demonstrate it's capabilities.
The Raspberry Pi is everything you would find in a desktop computer but really small. Build on the same basic platform as a smartphone, this little device can be connected to a monitor, keyboard, mouse, etc and be used like a regular computer. As well, it shares a lot of the same characteristics as the Arduino. It can be used with sensors and information from it's environment can be can be collected.