A cheesesteak sandwich, known outside of Philadelphia as a "Philly cheesesteak," is a sandwich with thinly-sliced steak meat and melted cheese. When served without cheese, it is simply known as a "steak sandwich."
The sandwich was invented by Pat and Harry Olivieri of Philadelphia, who served the sandwich on a hoagie-style bun. By 1930, the sandiwch was so popular that Pat Olivieri opened a cheesesteak restaurant that exists today, known as Pat's King of Steaks.
Despite being popular in its original steak and cheese form, variations of the sandwich often include grilled onions and bell peppers. Cheese Whiz is also a common option, which became popular in the early 1950s.
One of my guilty pleasures. I know they'll one day kill me, but I can't help myself. I love the taste of grilled roast beef and mozzarella on a roll. It's perfect to eat while watching a football game and wash down with beer! However, they're swimming in grease and calories, so it's an every now and then thing for me.