In addition to receiving live TV broadcast signal via the FreeView decoders which are typically built in to new TVs, via a separate service called "on-demand" consumers may now choose when and what to watch the from among offerings by various TV stations.
Basically, the TV stations may offer their library of programs for a period of weeks or years so the consumer can choose to view any of the offered programs. It's useful if you've missed a program or never bothered to check out one due to time restraints. It is a bit like the old visit to the DVD rental shop to pick your favourite video, except (A) it's free, (B) you don't have to visit anywhere, (C) there is no physical medium to hold, (D) the shows won't include movies, (E) do include adverts, (F) you need a good Internet connection, and finally (G) you need a device to intercept and view it with.
The adverts are far fewer than a live broadcast of the same thing – presumably because there is more assurance the consumer is watching the screen instead of just having the TV running idle in the background. Furthermore, the programs can't be recorded this way so the adverts can't be skipped, either.
The devices for intercepting and viewing on-demand shows till recently were limited to computers in their various forms (desktops, notebooks, tablets, mobiles etc) but are now offered with the FreeView decoders, including built into the TVs. So FreeViewPlus is the usual FreeView with on-demand built in. The biggest (and only?) advantage is that the on-demand library shows may now be played on a big TV screen via the FreeViewPlus TVs or FreeViewPlus boxes for use with old TVs.
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