Subtitling is the text version of onscreen dialogue, usually displayed at the bottom of the screen to help viewers who are hard of hearing to better follow the programme.
After switchover you will still be able to get the subtitling and signing services you get now and more. Most digital TV's and boxes have a dedicated 'subtitle' button for immediate access. To turn subtitling on Sky, press the 'help' button on the remote control and use the left/right buttons, then press 'select' to turn it on.
Find out more about what to look for in subtitling on products from Ricability.