Until I can write a more proper description, here's a quote from Wikipedia for you:
Wiki-tan said: Moe anthropomorphism (萌え擬人化, moe gijinka?) is a form of anthropomorphism where moe (basically, cute girl) qualities are given to non-human beings, objects, concepts, or phenomena; the subject of which often becomes a stylized anime girl, or bishōjo. In addition to moe features, moe anthropomorphizations are also characterized by their accessories, which serve to emphasize their original forms before anthropomorphosis. The female character here, usually in a kind of cosplay, is drawn to represent an inanimate object or popular consumer product. Part of the humor of this personification comes from the personality ascribed to the character (often satirical) and the sheer arbitrariness of identifying a variety of machines, objects, and even physical places as cute.