A Ferris wheel, named after George Washington Gale Ferris, Jr., (sometimes called a big wheel, observation wheel, or, in the case of the very tallest examples, giant wheel) is a nonbuilding structure consisting of a rotating upright wheel with multiple passenger-carrying components (commonly referred to as passenger cars, cabins, capsules, gondolas, or pods) attached to the rim in such a way that as the wheel turns, they are kept upright, usually by gravity.
Some of the largest modern Ferris wheels have cars mounted on the outside of the rim, with electric motors to independently rotate each car to keep it upright. These wheels may be referred to as observation wheels and their cars referred to as capsules. Sometimes these alternative names are also used for wheels with conventional gravity-oriented cars.
The original Ferris Wheel was designed and constructed by George Washington Gale Ferris, Jr. as a landmark for the 1893 World's Columbian Exposition in Chicago. The term Ferris wheel is used generically for all such structures which are now the most common type of amusement ride at state fairs in the United States.
Since the original 1893 Chicago Ferris Wheel there have been nine world's tallest-ever Ferris wheels. The current record holder is the 167.6-metre (550 ft) High Roller in Las Vegas, US, which opened to the public in March 2014.(Wikipedia)