Linked from
The 16 pages that link to Compressibility factor, each with the reason it gives.
Equation of stateRelated: It quantifies how strongly a real gas departs from ideal-gas predictions.
Ideal gasRelated: Its value shows how far a real gas is from the ideal model.
Real gasRelated: It quantifies how far a real gas departs from ideal behavior.
Gas lawsRelated: Quantifies deviations from ideal-gas behavior across conditions.