Tagging is fairly new. It means you may be allowed out of prison early if you agree to obey a curfew, that's a rule which says you can't leave your home at night.
To make sure you follow the rules you wear an electronic tag about the size of a fat digital watch. The tag sends a signal to a box connected to your phone. If you go out when you shouldn't the signal stops and the police are told the curfew has been broken.
Tagging is for prisoners with sentences of more than three months and less than four years. You have to be considered suitable and you must have a family home to go to during your curfew.
The government say that early release with a tag helps people fit back into society after prison. But not everyone is happy, some people think that the wrong kind of prisoners are being let out early.