Removed some...less than objective statements about Railgun. Original text preserved below:

Taken to silly levels in the To Aru Kagaku No Railgun anime, where more than half the run is filler. To be exact, episodes 3 and 13-24 are filler (Out of 24), (and other episodes have filler scenes as well) which means they could have cut the entire second half easily and there'd ve been no problems. Oh, wait, lead character Mikoto is very popular, better drag on this to sell more DVDs. It wouldn't have been so bad if the filler was good, but other than the Beach Episode (Which was episode 13, so once again, might as well have stopped with that) and the last arc, it was decent at best, with several one-shot episodes with little interest other than having Fan Service of (Guess who!) Mikoto and Kuroko (Uiharu and Saten fans might as well go look for ecchi pics), as well as contradicting canon (To the point a second season would need a few retcons to be possible) and the last arc's Filler Villain starting decent but ending as rather unoriginal. Sure, the original author penned it, but still. The stinger? This comes from an animation studio known mostly for compressing their adaptations (Such as Tora Dora), which makes the sudden 180-degree turnaround into Adaptation Expansion territory all the more strange.... or not.

What is a musical equivalent of Filler?

• The Asgard Arc of Saint Seiya. Later arcs (Poseidon, Hades) pick up the manga again, though.

"Filler is often misused to mean "any episode not in the original work", even if it's genuine Adaptation Expansion." You needs the Asgard arc to understand the Poseidon arc in the anime. In the anime, Saori was catched in the ending of the Asgard arc, thanks the events in the Asgard arc and the entry in the Poseidon Kingdom also is Asgard-dependent in the anime . In other words, not filler.

• Zatch Bell actually had quite little filler, especially if compared to other Toei productions. But then the anime almost Overtook The Manga, and the producers decided to make a completely anime-only arc, the Shion Arc. General consensus is that it's a very good arc, with interesting characters and a nice Tear Jerker.
  • The anime actually eliminated an important manga plot element, that the spellbooks told you how many demons were left, to incorporate filler. Raiku has acknowledged Wiseman (a movie-only demon) and Hyde (a demon who replaces Reycom as the first demon that Kiyomaro and Gash encounter), but no others.

• The Ranma One Half anime has a large amount of filler (including 3/5 of the seventh and final season), but in this case "filler" really means "original short story arcs unique to that canon". By the technical definition, the original manga was also full of filler... but neither version has a Myth Arc or, indeed, an overall storyline; Ranma 1/2 has its story arcs, but is pretty much episodic by definition. As in all cases, the quality of various filler stories ranges widely. For example, one technically filler episode manages to take Sasuke Sarugakure and not only make him interesting, but border-line tragic.
• The Oddly Named Sequel of Shugo Chara, Shugo Chara Doki, is yet only consisting of those. After the original series started getting DAMN close to Overtook The Manga, they started Doki with a pretty pointless filler arc about a french girl, who turns Shugo eggs into Question-mark-eggs. It finally finished after 39 episodes.
  • To be fair, the plot does continue while this arc is going on, albeit in an extremely dragged out manner. The big problem with Doki is that Lulu was only created to produce Monster Of The Week filler, so she sticks around for far too long and has a nasty habit of forgetting her Character Development when the episode only needs her as a plot device.

• Hayate No Gotoku's first season of 52 episodes contained almost as much anime-original filler as manga-based episodes. Given the nature of the show, many fans who hadn't read the manga often couldn't tell which was which.
  • Fortunately, the second season focuses more on the manga plot... sadly, to the point of skipping manga episodes and scenes that aren't vital to the plot. Until later on the run, then they have padding instead.

Filler not means "anime-only", but yes episode of Padding.

• After loosely following the manga for the first six episodes, the Kuroshitsuji/Black Butler anime adaptation consisted almost entirely of this for the remaining episodes. It is also notable for changing several important plot points and character traits.

Filler not means "not in the original work" but yes "episode of Padding".

• Even if the story quality is better than average for filler, the Bount Arc still creates continuity problems: There's no reason why Rukia's powers don't return immediately after the Soul Society arc (like they do in the manga), and in the anime, Hinamori takes an improbable amount of time to recover from her injuries from Aizen (she is a Lieutenant). There's the oddness with Ishida's powers too. Not to mention it's a major plot point in the Arrancar arc that Inoue didn't do much in the Soul Society Arc. In order for this to still work in the anime, she had to be useless in the Bount Arc too.

  • It also created leftover characters who became integrated into the canon arcs in the form of the three Mod Souls Ririn, Kurodo, and Nova

• The Slayers TRY season, while still helmed by the original creators, has a storyline not adapted from the original Light Novels. It dealt with a threat of Lina's world being destroyed by a Mazoku Lord from another universe, when said Dark Lord only had a small appearance in the original novels as the creator of Gourry's Sword of Light. The new season Slayers REVOLUTION returns to adapting events and characters from the novels that have not yet appeared.

Filler not means "not in the original work" but yes "episode of Padding