The Arduino is basically a prototyping platform, which makes use of an Atmel microprocessor - namely the ATmega range (ATmega8, ATmega168, ATmega328 etc..)
The Arduino _isn't_ a microprocessor - a microprocessor is placed into an Arduino board. The Arduino provides a way to interface with the microprocessor (via hardware ports, and a software interface).
The Arduino is basically a prototyping platform, which makes use of an Atmel microprocessor - namely the ATmega range (ATmega8, ATmega168, ATmega328 etc..)
The Arduino _isn't_ a microprocessor - a microprocessor is placed into an Arduino board. The Arduino provides a way to interface with the microprocessor (via hardware ports, and a software interface).