It means that more than likely you have been flashed by a speed camera or gone through a red light or committed another minor traffic offence.
The exact offence will be stated on the summons, along with the date of the court appearance - you must attend court on this date. If you can't attend, you must contact the court as soon as possible. You may be able to plead guilty by post to the alleged offence, the summons will explain your options.