To idolize is to admire someone too much. A twelve year-old might idolize a pop star, for example, wallpapering her bedroom with photos of him and screaming loudly throughout his concerts.
You can idolize someone you've never met, like a famous actor, and you can also idolize a friend or family member. A boy who idolizes his father adores him unquestioningly, believing that everything he does is admirable. Another way to say idolize is worship, and both words have a religious origin. In the case of idolize, the root word is idol, or "image of a god used in worship," from the Late Latin word idolum, "image or form."