A novelization is the retelling, in novel form, of another story that was told by some other means than prose (movie script, poem, theatrical play, audio recording, computer game, etc.). The novelization is thus not an original work. The retold story might be expanded from its original form with additional scenes and background material, all such material being within canon and approved by the copyright holders of the original work.
In Daria fandom, the term novelization is used to describe a prose work that retells the story presented in one of the TV episodes or movies (e.g., "Antisocial Climbers"). Such tales do not rise to the level of a true novel, almost always being short stories. Prose adaptations are easier for many fans to read than are episode scripts.
In addition to official episodes being novelized, popular scriptfics by other fans are at times given this treatment. Canadibrit's The Look-Alike Series (TLAS) has had many script-based episodes novelized by its fans.