LED stands for Light Emitting Diode. Currently, it and OLED are the only form of Solid State Lighting (No Filament) available.
LED's create very little heat when they use the input energy to make visible light. The light made is passed through a Phosphorous coating to turn the light to the proper spectrum desired. In manufacturing, it will get packaged into what is called a chip . This term is commonly referred to in LED fixtures and is asking what type of LED is used.
LED's can be found in a variety of different types, including: High Power LED's, Mid Power LED's, COB LED's, SMD LED's, and more less common types.