An "indicator" is a measurable variable that provides information about a specific condition or trend. It is often used in various fields such as economics, health, and environmental science to assess performance or progress. For example, the Gross Domestic Product (GDP) is an economic indicator that reflects the overall economic activity of a country. Indicators can be quantitative, like statistics, or qualitative, like surveys. They help decision-makers understand complex situations and make informed choices. In public health, indicators like infant mortality rates can reveal the effectiveness of healthcare systems and guide policy improvements.