Define the term 'thermal expansion' in plumbing systems.

Thermal expansion refers to the increase in volume that occurs when water (or any liquid) is heated. In plumbing systems, as water is heated, its molecules move faster and spread apart, resulting in an increase in volume. This property is significant because it can affect the integrity and functionality of piping systems.

When water in pipes heats up, the resulting increase in volume can lead to higher pressure within the pipes. If not properly accommodated, this can cause stress on the pipes and joints, potentially leading to leaks or bursts. Therefore, understanding thermal expansion is critical for designing plumbing systems that can handle the changes in volume that occur with temperature fluctuations.

By selecting materials and systems that allow for movement due to thermal expansion, plumbers can help ensure the longevity and reliability of plumbing installations.