A limousine by definition is a luxury sedan or saloon driven by a chauffeur. Limousine or limo is the description now used to describe a modified stretched version on luxury saloon or sedan and they are usually chauffeured. Stretching limousines is not a easy as just inserting a piece in. Much consideration has to be given to the extra stress on the overall body, brakes, engine and transmission. The vehicles when loaded with passengers plus the additional body work can double their initial weight. Before stretching a vehicle the engineering certificates have to be approved by the relevant governing bodies.
Over many years the Lincoln limousines have proved very popular and were used by several Presidents of the USA. Elvis Presley owned his own private Lincoln limousine.
A Hummer is described as a Sports Utility Truck so whether this is limo or not when stretched is open to debate. https://en.wikipedia.org/wiki/Hummer_H2