The combined gas law is a fundamental equation in chemistry that relates the pressure, volume, and temperature of a gas. It combines Boyle's Law, Charles's Law, and Gay-Lussac's Law into a single formula: $$\frac{P_1V_1}{T_1} = \frac{P_2V_2}{T_2}$$. This law is essential for understanding the behavior of gases under varying conditions and connects various properties of gases to the ideal gas law.