According to "New Oxford American Dictionary," the name "sedan" comes from the Latin word "sedere," which means to sit, and also "sella," which means saddle. It's a fitting name for the sedan, as it's a car that's associated with a comfortable interior and a smooth ride. 

The name derives from the 17th-century litter known as a sedan chair, a one-person enclosed box with windows and carried by porters. 

A sedan is designed as a 3-box configuration vehicle — engine, passenger and cargo. The word sedan is used in American English, while the word saloon is used in British English. As for notchbacks, these are sedans with a less pronounced boot or trunk space. They are sedans with a hatchback rear. 

The word "sedan" was first used to describe an automobile body in 1912. However, the word had been used to describe a covered chair carried by multiple people since the 17th century. 

1 hour ago, Bill W said:

A sedan is designed as a 3-box configuration vehicle — engine, passenger and cargo. The word sedan is used in American English, while the word saloon is used in British English. As for notchbacks, these are sedans with a less pronounced boot or trunk space. They are sedans with a hatchback rear.

In Australian English that type of car is referred to as a sedan. Saloon car is included in the Macquarie Dictionary but it's use now is generally confined to a particular type of motor racing. Cars with a hatchback rear are referred to simply as hatchbacks.