Isochoric: The volume of the system remains constant throughout a process.
Ex. If you heat a gas in a closed, rigid container, the volume of the gas will stay the same even as temperature and pressure change.
Isobaric: The pressure of the system remains constant throughout a process.
Ex. You blow air into a balloon. The balloon expands so that the internal pressure remains constant. The volume changes but the pressure is constant.
Isothermal: The temperature of the system stays constant through a reaction.
Ex. Melting (as well as all other phase changes) is isothermal. As a substance transitions from the solid to liquid phase, the added energy is used to weaken attractions, not change temperature. Thus, temperature remains constant.
Chemistutor 