Markers, or indicators, are measurable signs that provide information about a specific condition or trend. They are often used in various fields, such as economics, healthcare, and environmental science, to assess performance or changes over time. For example, in economics, the Gross Domestic Product (GDP) is a key indicator of a country's economic health. In healthcare, markers can refer to biological indicators, such as cholesterol levels or blood pressure, that help assess an individual's health status. Similarly, in environmental science, indicators like air quality index or biodiversity levels help gauge the health of ecosystems. These markers are essential for making informed decisions and tracking progress.