The document discusses harmonics in electrical systems. Harmonics refer to voltages or currents at frequencies that are multiples of the fundamental supply frequency, such as 50 Hz or 60 Hz. They can be caused by non-linear loads like variable frequency drives, UPS systems, and electronic equipment that draw current in pulses rather than smoothly. The presence of harmonics can reduce equipment life, cause overheating, and increase energy losses. It is important to analyze power quality and minimize harmonics through proper protection devices. The document advertises contact information for a company that performs harmonics audits.