While you are using Facebook many Apps are asking to access your account in order to use them. It's always a good idea to clean Applications that you no longer use or those which you don't want to have access in your profile's photos, messages, friends etc. So go to your Facebook Application Settings.
Here you will find a list with all the Apps that have access in your account.
If you click on an App you can see exactly where this App has access to and when it last accessed your account.
To remove an Application you no longer need simply press the X button and confirm.