What is a protein-rich fluid containing white blood cells and cell debris known as?

The term commonly used to describe a protein-rich fluid that contains white blood cells and cell debris is "pus." Pus is typically associated with infections or inflammation, where the body sends white blood cells to the site of infection to combat pathogens. The accumulation of these immune cells, along with tissue debris and fluid, forms pus, which is often found in abscesses or infected wounds.

In contrast, exudate refers to a fluid that leaks out of blood vessels due to injury or inflammation, and it can be high in protein, but it does not specifically denote the presence of cellular debris that is characteristic of pus. Serum is the clear, yellowish fluid that remains after blood coagulates and contains plasma proteins, but it does not include white blood cells or debris. Transudate is a fluid that results from systemic conditions that alter hydrostatic or oncotic pressure and is typically low in protein and cellular content, distinguishing itself from pus both in composition and origin.

Thus, the defining characteristics of pus make it the correct answer, as it is explicitly recognized for containing the components associated with infection and inflammation.