Being in a "fat-burning zone" refers to exercising at a moderate intensity where the body utilizes a higher percentage of fat as a fuel source compared to carbohydrates. This zone is generally defined as being around 60-70% of an individual's maximum heart rate. While the absolute calories burned might be lower than at higher intensities, fat oxidation is enhanced. However, it's important to note that total calorie expenditure is crucial for weight loss, and incorporating varying intensities can optimize overall fat loss and fitness benefits.