SMD = Surface Mount Device, that is, a chip LED, transistor, capacitor, resistor
As opposed to an axial lead device, those 2-contact devices with a solid, rigid wire emerging from each end of the resistor or capacitor or diode
On another note: Each colour of LED & size requires different energy. Each colour requires a certain voltage across the internal LED junction. The difference between the power source voltage & what the LED requires is absorbed by the series resistor, often referred to as the ballast resistor.