Lean body mass refers to the weight of everything in the body except fat. This includes muscles, bones, organs, and water. It is an important measure for assessing overall health and fitness, as higher lean body mass is often associated with better metabolism and physical performance. Maintaining or increasing lean body mass can be achieved through regular exercise, particularly strength training, and a balanced diet rich in protein. Understanding lean body mass can help individuals set fitness goals and track their progress, making it a valuable concept in health and wellness discussions.