The 1800s (pronounced "eighteen-hundreds") was a decade of the Gregorian calendar that began on 1 January 1800, and ended on 31 December 1809.
The term "eighteen-hundreds" could also mean the entire century from 1 January 1800 to 31 December 1899 (the years beginning with "18"), and is almost synonymous with the 19th century (1801–1900).