"Rest days" in a fitness regimen refer to designated days where individuals intentionally refrain from intense physical activity to allow for recovery and muscle repair. These days are crucial for preventing overtraining and reducing the risk of injuries, as they give muscles time to recuperate and adapt after strenuous exercise. Incorporating rest days into a workout schedule can also enhance overall performance, as the body rebuilds and strengthens during these periods. Active recovery activities, such as light stretching or walking, can complement rest days without exerting excess strain on the body.