The International Standard Industrial Classification of All Economic Activities, known as ISIC Rev. 4, is a system developed by the United Nations to categorize economic activities. It provides a framework for collecting and analyzing data related to industries, facilitating comparisons across countries and over time. ISIC Rev. 4 classifies activities into 21 sections, ranging from agriculture to services, using a hierarchical structure. This classification helps governments, researchers, and businesses understand economic trends and make informed decisions based on industry performance and development.