A century is a period of 100 years. It is commonly used to measure time in history, allowing us to categorize events and developments. For example, the 20th century refers to the years from 1901 to 2000, while the 21st century began in 2001 and will end in 2100. Centuries are often divided into decades, which are 10-year periods. Each century can be associated with significant cultural, technological, and political changes. For instance, the Industrial Revolution occurred during the 18th and 19th centuries, transforming economies and societies around the world.