# Century

A century is a period of 100 years or 10 decades. Centuries are numbered ordinally in English and many other languages. The word century comes from the Latin centum, meaning one hundred. Century is sometimes abbreviated as c.
A centennial or centenary is a hundredth anniversary, or a celebration of this, typically the remembrance of an event which took place a hundred years earlier.

## Start and end of centuries

Although a century can mean any arbitrary period of 100 years, there are two viewpoints on the nature of standard centuries. One is based on strict construction, while the other is based on popular perception.
According to the strict construction, the 1st century AD, which began with AD 1, ended with AD 100, and the 2nd century with AD 200; in this model, the n-th century starts with a year that follows a year with a multiple of 100 (except the first century as it began after the year 1 BC) and ends with the next coming year with a multiple of 100 (100n), i.e. the 20th century comprises the years 1901 to 2000, and the 21st century comprises the years 2001 to 2100 in strict usage.
In common perception and practice, centuries are structured by grouping years based on sharing the 'hundreds' digit(s). In this model, the n-th century starts with the year that ends in "00" and ends with the year ending in "99"; for example, in popular culture, the years 1900 to 1999 constitute the 20th century, and the years 2000 to 2099 constitute the 21st century. (This is similar to the grouping of "0-to-9 decades" which share the 'tens' digit.)
To facilitate calendrical calculations by computer, the astronomical year numbering and ISO 8601 systems both contain a year zero, with the astronomical year 0 corresponding to the year 1 BC, the astronomical year -1 corresponding to 2 BC, and so on.
Strict vs Popular usage :
| Year | 2 BC | 1 BC | 1 | 2 | ... | 99 | 100 | 101 | 102 | ... | 199 | 200 | 201 | 202 | ... | 1899 | 1900 | 1901 | 1902 | ... | 1999 | 2000 | 2001 | 2002 | ... | 2025 | ... | 2099 | 2100 | 2101 | 2102 | ... |
| Strict | 1st century BC | 1st century BC | 1st century | 1st century | 1st century | 1st century | 1st century | 2nd century | 2nd century | 2nd century | 2nd century | 2nd century | 3rd century | 3rd century | ... | 19th century | 19th century | 20th century | 20th century | 20th century | 20th century | 20th century | 21st century | 21st century | 21st century | 21st century | 21st century | 21st century | 21st century | 22nd century | 22nd century | ... |
| Popular | 1st century BC | 1st century BC | 1st century | 1st century | 1st century | 1st century | 2nd century | 2nd century | 2nd century | 2nd century | 2nd century | 3rd century | 3rd century | 3rd century | ... | 19th century | 20th century | 20th century | 20th century | 20th century | 20th century | 21st century | 21st century | 21st century | 21st century | 21st century | 21st century | 21st century | 22nd century | 22nd century | 22nd century | ... |

## Alternative naming systems

Informally, years may be referred to in groups based on the hundreds part of the year. In this system, the years 1900–1999 are referred to as the nineteen hundreds (1900s). Aside from English usage, this system is used in Swedish, Danish, Norwegian, Icelandic, Finnish and Hungarian. The Swedish nittonhundratalet (or 1900-talet), Danish nittenhundredetallet (or nittenhundredetallet), Norwegian nittenhundretallet (or 1900-tallet), Finnish tuhatyhdeksänsataaluku (or 1900-luku) and Hungarian ezerkilencszázas évek (or 1900-as évek) refer unambiguously to the years 1900–1999. In Swedish, however, a century is in more rare cases referred to as det n-te seklet/århundradet ("the n-th century") rather than n-hundratalet, i.e. the 17th century is (in rare cases) referred to as 17:(d)e/sjuttonde århundradet/seklet rather than 1600-talet and mainly also referring to the years 1601–1700 rather than 1600–1699; according to Svenska Akademiens ordbok, 16:(d)e/sextonde århundradet may refer to either the years 1501–1600 or 1500–1599.

## Similar dating units in other calendar systems

While the century has been commonly used in the West, other cultures and calendars have utilized differently sized groups of years in a similar manner. The Hindu calendar, in particular, summarizes its years into groups of 60, while the Aztec calendar considers groups of 52.