SS Great Eastern was an iron sail-powered, paddle wheel and screw-propelled steamship designed by Isambard Kingdom Brunel, and built by John Scott Russell & Co. at Millwall Iron Works on the River Thames, London, England. She was by far the largest ship ever built at the time of her 1858 launch, and had the capacity to carry 4,000 passengers from England to Australia without refuelling. Her length of 692 feet (211 m) was surpassed only in 1899 by the 705-foot (215 m) 17,274-gross-ton RMS Oceanic, her gross tonnage of 18,915 was only surpassed in 1901 by the 701-foot (214 m) 20,904-gross-ton RMS Celtic and her 4,000-passenger capacity was surpassed in 1913 by the 4,234-passenger SS Imperator. The ship having five funnels was unusual for the time. The vessel also had the largest set of paddle wheels.

A steamship, often referred to as a steamer, is a type of steam-powered vessel, typically ocean-faring and seaworthy, that is propelled by one or more steam engines that typically move (turn) propellers or paddlewheels. The first steamships came into practical usage during the early 1800s; however, there were exceptions that came before. Steamships usually use the prefix designations of "PS" for paddle steamer or "SS" for screw steamer. As paddle steamers became less common, "SS" is incorrectly assumed by many to stand for "steamship". Ships powered by internal combustion engines use a prefix such as "MV" for motor vessel, so it is not correct to use "SS" for most modern vessels.