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This definition differs from the standard definition. The New Oxford American Dictionary defines it as
a digital recording of a radio broadcast or similar program, made available on the Internet for downloading to a personal audio player
My emphasis on the word usually underscores the point made two slides later -- you don't need an iPod. If a teacher finds a useful podcast episode, the teacher can carry it into a classroom on a CD. Students in a computer lab can listen through the computer. And so on.