The Heat Index is a measure that combines air temperature and humidity to determine how hot it feels to the human body. It is often referred to as the "apparent temperature" because it accounts for the body's ability to cool itself through sweating. When humidity is high, sweat does not evaporate as easily, making it feel hotter than the actual air temperature. The Heat Index is important for understanding heat-related health risks. High Heat Index values can lead to heat exhaustion or heat stroke, especially for vulnerable populations like the elderly or those with certain medical conditions. Monitoring the Heat Index helps individuals take precautions during hot weather, such as staying hydrated and avoiding strenuous activities.