The best description about the arduino project comes from their own website:
“Arduino is an open-source electronics prototyping platform based on flexible, easy-to-use hardware and software. It’s intended for artists, designers, hobbyists, and anyone interested in creating interactive objects or environments.”
But unfortunately they forgot about scientists!! This is a great platform for:
-Learning a little bit of electronics which is always handy in a laboratory, whether you simply want to understand how that PCR machine really works or to understand how to fix that damn TTL pulse that is constantly failing.
-Building full operational setups at much lower cost than the current commercial systems, one arduino UNO board cost ~50€ and a beginner kit, with LEDs, buttons, resistors and other sensors can be bought for around ~60€.
To put in more practical words, the Arduino is a micro controller that has several digital inputs/outputs as well as analog inputs and also outputs. It runs up to 16MHz of speed, and is normally programmed with a special designed language, that is actually a simplified version of C++, which can also be used instead (for people who already know how to program in c++).
There is a nice series of videos from the people of Fritzing, showing how to get started with eletronics and the Arduino