What is the definition of "studio apartment"?

A studio apartment is an apartment consisting of one single main room plus a bath. They may or may not include a small kitchen as a separate room.

Studio apartments can be a range of sizes and are a good choice for students or singles, or they can be used as a second apartment for those who travel often and need a place to sleep. Studio apartments in the U.S. are typically 600 square feet in size, but can be as small as 300 square feet. Studio apartments are generally lower in cost than other apartments because they have fewer rooms. Luxury studio apartments, which are one-room apartments with higher ceilings and larger square footage, are now commonly referred to as "lofts".