How is "glycogen" best defined?

Glycogen is best defined as a form of stored glucose in the liver and muscles. It serves as a crucial energy reserve that can be quickly mobilized when the body needs a rapid source of glucose, especially during physical activity. Glycogen is a polysaccharide composed of many glucose units linked together, which allows it to be efficiently stored and later broken down into glucose when energy is required.

In the liver, glycogen can be converted back into glucose to maintain steady blood sugar levels, while in muscle tissue, it's readily available to fuel muscle contractions during exercise. This specific role differentiates glycogen from fats, proteins, and minerals, highlighting its importance in energy metabolism.