An isothermal process is a thermodynamic process that occurs at a constant temperature. During this process, the system exchanges heat with its surroundings to maintain the same temperature while doing work. This means that any energy added to the system as heat is balanced by the work done by the system, keeping the internal energy unchanged. A common example of an isothermal process is the expansion of a gas in a piston at a constant temperature. In this scenario, as the gas expands, it absorbs heat from the surroundings, allowing it to do work on the piston without changing its temperature.