A "blue flame" refers to the color of the flame produced by certain fuels when they burn completely. This phenomenon occurs when there is a sufficient supply of oxygen, allowing for efficient combustion. Common sources of blue flames include natural gas and propane, which are often used in stoves and heaters. The blue color indicates that the fuel is burning at a high temperature and is producing fewer pollutants, such as carbon monoxide. In contrast, a yellow or orange flame typically signifies incomplete combustion, which can release harmful substances into the air. Proper ventilation is essential for achieving a blue flame in appliances like gas stoves and furnaces.