A restaurant "is a business which prepares and serves food and drinks to customers in exchange for money."
McDonalds prepares and serves food and drinks to customers in exchange for money. This clearly makes it a restaurant. It may not be a fine-dining type of establishment, but it is a restaurant.
More pretentious is all the hipsters that look down on restaurants like McDonalds simply because it doesn't fit their narrow, preconceived notions of what a restaurant should be.
McDonalds prepares and serves food and drinks to customers in exchange for money. This clearly makes it a restaurant. It may not be a fine-dining type of establishment, but it is a restaurant.
More pretentious is all the hipsters that look down on restaurants like McDonalds simply because it doesn't fit their narrow, preconceived notions of what a restaurant should be.