Seven segment Displays are very common when it comes to display digits, these are widely used in clocks, stop watches and event counter etc. A Simple seven segment display is shown in the image below..
This is a front view..
And this is back view...
The seven segment display as the name implies consist of 7 Leds, these 7 leds together can form any number from 0 to 9 as shown below..
Below is shown a model where 7 leds are placed in such a way that they can form any digit..
This seven segment display is a 10 pin component.. these pins are basically for each LED, for decimal LED (DOT which is shown above) and also for ground/power connection.