Western civilization is a conglomerate and aggregation of the best parts of many
Much of it was funded by pillaging or otherwise subsuming the husbanded resources, useful methods and ideas, and often sophisticated artifacts of other more developed cultures. The term Western civilization is a catchall to refer to the many cultures of European heritage that share common cultural ideas, philosophical foundations, and ancestral beliefs. Basically, the idea is that these cultures all have a common heritage, which has been important in the development of each. This concept is sometimes used in contrast to so-called Eastern civilization, explaining the basic differences underlying cultures of Europe and Asia. That's the basic definition, but what does this really mean? For that, we'll have to go a little deeper into the West.
Its roots lay in the civilizations of ancient Greece and Rome (which themselves built on foundations laid in ancient Egypt and Mesopotamia). It took shape in medieval Europe, with its Christian religion, feudal society, dispersed power-structures and growing economic dynamism. It was in the modern era that Western civilization took flight, however. It spread from Europe to the Americas, Australasia and much of the rest of the world; it achieved a level of economic power which far surpassed that of any other civilization; it developed the habit of systematic scientific and technological advance; and it evolved a unique set of personal freedoms which gave its culture an utterly different flavour to anything that had come before.