user20: Since just "ending" can have both meanings, we should differentiate questions about the actual anime ending (maybe tag with plot?) and the ending song / theme / ED (ending-song?).
What should the tags be?

user28: I think it would be better to use a tag that represents both the intro and outro songs, maybe something along the lines of "theme song", then the OP can describe which one or both they are referring to.

user111: "ending-song" implies that the tag is about the song, but there is also video there, so that doesn't make absolute sense, thus I wouldn't vote for renaming it like that. Also I'd say that the most used meaning of "ending" would be the episode's ending (song, that is) rather than the anime's plot ending. 
So, I'd suggest leaving the "opening" and "ending" tags for the episode's opening and ending (i.e. songs), and making either "plot-ending" or "story-ending" for the story (IMO "story-ending" sounds a bit better).
I think two synonyms should be created as well: "OP" for "opening" and "ED" for "ending".
Note that it may be also useful to have tags for the music only, maybe "soundtrack" or "original-soundtrack" ( with a synonim "OST" ) tag for the soundtrack-related questions. Or maybe it should be names as simple as "music".

user63: For music related to an anime, wouldn't it be easier just to bundle then into one all-encompassing music?  
Although most questions will probably concern OPs and EDs, sometimes there may be questions concerning insert songs, like "Alchemy" in Angel Beats or "God Knows" in Haruhi. 
We can then add opening-theme, ending-theme, insert-song, and/or character-theme tag synonyms.

20: <p>Since just "ending" can have both meanings, we should differentiate questions about the actual anime ending (maybe tag with <a href="https://anime.stackexchange.com/questions/tagged/plot" class="post-tag" title="show questions tagged &#39;plot&#39;" rel="tag">plot</a>?) and the ending song / theme / ED (<a href="https://anime.stackexchange.com/questions/tagged/ending-song" class="post-tag" title="show questions tagged &#39;ending-song&#39;" rel="tag">ending-song</a>?).</p>

<p>What should the tags be?</p>
 28: <p>I think it would be better to use a tag that represents both the intro and outro songs, maybe something along the lines of "theme song", then the OP can describe which one or both they are referring to.</p>
 111: <p>"ending-song" implies that the tag is about the <em>song</em>, but there is also video there, so that doesn't make absolute sense, thus I wouldn't vote for renaming it like that. Also I'd say that the most used meaning of "ending" would be the episode's ending (song, that is) rather than the anime's plot ending. </p>

<p>So, I'd suggest leaving the "opening" and "ending" tags for the episode's opening and ending (i.e. songs), and making either "plot-ending" or "story-ending" for the story (IMO "story-ending" sounds a bit better).</p>

<p>I think two synonyms should be created as well: "OP" for "opening" and "ED" for "ending".</p>

<p>Note that it may be also useful to have tags for the music only, maybe "soundtrack" or "original-soundtrack" ( with a synonim "OST" ) tag for the soundtrack-related questions. Or maybe it should be names as simple as "music".</p>
 63: <p>For music related to an anime, wouldn't it be easier just to bundle then into one all-encompassing <a href="https://anime.stackexchange.com/questions/tagged/music" class="post-tag" title="show questions tagged &#39;music&#39;" rel="tag">music</a>?  </p>

<p>Although most questions will probably concern OPs and EDs, sometimes there may be questions concerning insert songs, like "Alchemy" in <em>Angel Beats</em> or "God Knows" in <em>Haruhi</em>. </p>

<p>We can then add <a href="https://anime.stackexchange.com/questions/tagged/opening-theme" class="post-tag" title="show questions tagged &#39;opening-theme&#39;" rel="tag">opening-theme</a>, <a href="https://anime.stackexchange.com/questions/tagged/ending-theme" class="post-tag" title="show questions tagged &#39;ending-theme&#39;" rel="tag">ending-theme</a>, <a href="https://anime.stackexchange.com/questions/tagged/insert-song" class="post-tag" title="show questions tagged &#39;insert-song&#39;" rel="tag">insert-song</a>, and/or <a href="https://anime.stackexchange.com/questions/tagged/character-theme" class="post-tag" title="show questions tagged &#39;character-theme&#39;" rel="tag">character-theme</a> tag synonyms.</p>
