The apple logo refers to the bite adam and eve took out of an apple from the tree of knowledge

The, now well-known, American company Apple was the first computer firm not to use its name as its corporate identity. The idea of selling a computer under the name and image of a fruit was conceived by Californian Steve Jobs and his colleagues (even the word "Macintosh" is the name of an apple variety). The motif of a multicolored apple with a bite taken out of it is a reference to the Bible story of Adam and Eve, in which the apple represents the fruit of the Tree of Knowledge. For more information about the logos, read this interesting article

http://www.dinesh.com/History_of_Logos/Information_Technology_(IT)_Logos_-_Design_and_History/Apple_Logo_-_Design_and_History/