Compound exercises use multiple joints and muscle groups in a single movement — squats, deadlifts, bench press, rows, pull-ups. Isolation exercises target one muscle group through a single joint — bicep curls, leg extensions, lateral raises. Compounds are the foundation of any serious training program because they produce the most stimulus per unit of time. Isolation exercises are the detail work — targeting specific muscles that compounds may not fully develop. Most people need both. The question is how to balance them.