Most Helpful Guy
The difference between milkshakes and smoothies are that milkshakes usually consist of *only* dairy products (and flavoring), while smoothies are made of both dairy products and real fruit.
Slushies are entirely different because they are essentially frozen soda. They're just made with ice and flavored syrup.
Most Helpful Girl
Milkshakes are ground up ice cream with milk mixed in, smoothies are ground up fruit, and slushies are grinded ice with sweet flavored syrup.