Any change from the original source material to its adaptation, be it a new character, a new scene, a new location, a character performing a different action than they did in the source material, a new/different/changed plot or subplot, etc. Usually from books
but may apply to any adaptation that is not a reboot
and instead simply alters some of the source material.
Ros on Game of Thrones
is shownly as she is not in the A Song of Ice And Fire
Will is shownly a working songwriter on the TV show and not the book or movie versions of About A Boy.
The sponsor gifts coming with notes from Haymitch is shownly in The Hunger Games
The romance between Grey Worm and Missandei is shownly.