Ubiquitous Computing can be thought of as the idea of invisible computers everywhere. Specifically,it is the idea that computers are embedded in the environment, 
with literally dozens or hundreds of computers available to each person, and each computer performing its tasks without requiring human awareness or a large amout of human intervention. If the mainframe represents the era of "many people, one computer", and the PC is the era of "one person, one computer", then ubiquitous computing can be thought of as the era of "one person, many computers".
