Boyle's law is a gas law that describes how the pressure and volume of a gas are inversely proportional to each other, at a constant temperature. In other words, as the volume of a gas decreases, its pressure increases, and vice versa, as long as temperature remains constant.
The important thing to hold constant in order for Boyle's law relationship to work is the temperature. If the temperature of the gas changes, then the relationship between pressure and volume described by Boyle's law no longer holds.