The display uses seven (7) segments in order to represent the decimal numbers 0-9. The numbers are formed when they light some of the parts of the seven segment display.
There are displays which use light emitting diodes (LEDs) for the construction of their segments. They are constructed in two types, common anode where all the diode anodes of the segments are connected together and the ones of the common cathode where all the cathode diodes of the segments are commonly connected.