Digital copy is sometimes included with the purchase of a DVD or Blu-ray and is an additional digital file of the film/TV show. This is either included on one of the discs, or a unique code is given to download the file online. You can then transfer the file onto your computer or portable media player.
The disc typically comes with a single-use code to authenticate a computer over the internet. Alternatively, content owners can offer the digital copy feature as a paid service. Often the authentication code has an expiration date rendering the copy invalid if unused before this time.
The exact use and availability of digital copy varies by title, and it depends which studio is releasing the title. There should be a paper insert inside the case of DVD or Blu-ray that includes digital copy and this will outline the different elements of the copy. If there isn't an insert or if you need to clarify details of the copy, you should contact the studio directly.
Many digital copies are stored on a physical disc but some may need to be downloaded from an online source. Read your disc's insert for details. Digital copies may have an expiry date for when you can download the copy by. Check your insert for dates. If the date has passed, you won't be able to download the digital copy.
Products purchased in the UK are often geographically limited, and as such they might only work in the UK and Ireland. This does vary title-by-title, and if you want to download the digital copy outside of the UK and Ireland, you should refer to the insert for details or check with the studio directly.