What is a Led matrix display?

A Led matrix display for example 8*8 leds is an array of leds connected in a special manner to be driven with a special way

For example at the back of this matrix there is 8 pins for rows and 8 pins for columns

if you want to make the first column "on" you should put +5V on the 8 rows and put a ground on the pins corresponding to first column .