A British thermal unit, or BTU, is a unit of measurement used to quantify heat energy. Specifically, it represents the amount of energy needed to raise the temperature of one pound of water by one degree Fahrenheit. BTUs are commonly used in heating and cooling systems, such as air conditioners and furnaces, to indicate their energy output or efficiency. In practical terms, BTUs help consumers understand how much energy appliances consume and how effectively they can heat or cool a space. For example, a central air conditioning unit may be rated in BTUs to show its cooling capacity, allowing homeowners to choose the right size for their needs.