Cook and Chef, what is the difference?

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I am confused about what they call Cook or a chef. As I see and hear, cooks are found in a small eatery, small restaurant businesses, sidewalk fastfood and or in a fastfood chain people call them cook/s. while Chefs are in a middle class restaurants, Hotels, luxury cruisers, Fine dining restaurants, and they call them Chef/s. Can anyone connect me to this?.. Is there a discrimination even in preparing Peoples meal?! LOL!