Boiling, in the context of nuclear reactors, refers to the process where water is heated within the reactor core until it turns into steam. This steam is then used to drive turbines that generate electricity. In boiling water reactors (BWRs), water serves both as a coolant, absorbing heat from the nuclear reaction, and as a moderator, slowing down neutrons to sustain the reaction. The direct production of steam inside the reactor core distinguishes BWRs from other reactor types, making the boiling process central to their operation.