user4: The initial days of beta can be a little awkward for tags. This post is meant to be a community-wiki style list of tags that need to be cleaned up for cases where users (like me) don't have sufficient reputation to make the changes.
Please feel free to edit my answer and add any changes you see need to be made (or remove any changes that have been completed)

user4: Spelling errors

webserver should be web-server
r should be r-environment One letter tags tend to be confusing Language tags should always be the language name, till the point a conflict arises.

Merges

uno and arduino-uno should be the same (pending discussion)
due with arduino-due
The upload tag should be merged into the more established uploading tag.


user24: Irrelevant Tags
These tags are mostly accidentally created and should be removed.

c++ Discussion Here


Vague Tags
These should be removed (maybe even blocked if there is an option in the SE engine) because they are too vague.

input Too vague. The question that uses it uses it fine, but it really doesn't help someone find that question, and interrupts should be sufficient.
ide should be split into arduino-ide and individual tags such as eclipse


Spelling
These tags are mostly ones that need to be separated with a "-".
[None]

Synonyms
Synonyms require significant reputation or moderator abilities to create. The "master tag" (or whatever the proper term is) will replace the synonym when typed.

atmega328 I don't know what to do about this one really but often people tag this along with uno/arduino-uno
build → compile Some beginners may tag it as build but for the physical construction of a project. Mods have decided to leave it and watch it.


Tags to watch in the future...
Tags for topics that may be deemed off-topic soon.

enclosure Will we allow shopping questions here?


4: <p>The initial days of beta can be a little awkward for tags. This post is meant to be a community-wiki style list of tags that need to be cleaned up for cases where users (like me) don't have sufficient reputation to make the changes.</p>

<p>Please feel free to edit my answer and add any changes you see need to be made (or remove any changes that have been completed)</p>
 4: <h2>Spelling errors</h2>

<ul>
<li><a href="https://arduino.stackexchange.com/questions/tagged/webserver" class="post-tag" title="show questions tagged &#39;webserver&#39;" rel="tag">webserver</a> should be <a href="https://arduino.stackexchange.com/questions/tagged/web-server" class="post-tag" title="show questions tagged &#39;web-server&#39;" rel="tag">web-server</a></li>
<li><s><a href="https://arduino.stackexchange.com/questions/tagged/r" class="post-tag" title="show questions tagged &#39;r&#39;" rel="tag">r</a> should be <a href="https://arduino.stackexchange.com/questions/tagged/r-environment" class="post-tag" title="show questions tagged &#39;r-environment&#39;" rel="tag">r-environment</a> One letter tags tend to be confusing</s> <em>Language tags should always be the language name, till the point a conflict arises.</em></li>
</ul>

<h2>Merges</h2>

<ul>
<li><a href="https://arduino.stackexchange.com/questions/tagged/uno" class="post-tag" title="show questions tagged &#39;uno&#39;" rel="tag">uno</a> and <a href="https://arduino.stackexchange.com/questions/tagged/arduino-uno" class="post-tag" title="show questions tagged &#39;arduino-uno&#39;" rel="tag">arduino-uno</a> should be the same (<a href="https://arduino.meta.stackexchange.com/questions/3/4">pending discussion</a>)</li>
<li><a href="https://arduino.stackexchange.com/questions/tagged/due" class="post-tag" title="show questions tagged &#39;due&#39;" rel="tag">due</a> with <a href="https://arduino.stackexchange.com/questions/tagged/arduino-due" class="post-tag" title="show questions tagged &#39;arduino-due&#39;" rel="tag">arduino-due</a></li>
<li>The <a href="https://arduino.stackexchange.com/questions/tagged/upload" class="post-tag" title="show questions tagged &#39;upload&#39;" rel="tag">upload</a> tag should be merged into the more established <a href="https://arduino.stackexchange.com/questions/tagged/uploading" class="post-tag" title="show questions tagged &#39;uploading&#39;" rel="tag">uploading</a> tag.</li>
</ul>
 24: <h2>Irrelevant Tags</h2>

<p>These tags are mostly accidentally created and should be removed.</p>

<ul>
<li><a href="https://arduino.stackexchange.com/questions/tagged/c%2b%2b" class="post-tag" title="show questions tagged &#39;c++&#39;" rel="tag">c++</a> <a href="https://arduino.meta.stackexchange.com/questions/111/when-should-we-use-the-c-tag">Discussion Here</a></li>
</ul>

<hr>

<h2>Vague Tags</h2>

<p>These should be removed (maybe even blocked if there is an option in the SE engine) because they are too vague.</p>

<ul>
<li><a href="https://arduino.stackexchange.com/questions/tagged/input" class="post-tag" title="show questions tagged &#39;input&#39;" rel="tag">input</a> Too vague. The question that uses it uses it fine, but it really doesn't <em>help</em> someone find that question, and interrupts should be sufficient.</li>
<li><a href="https://arduino.stackexchange.com/questions/tagged/ide" class="post-tag" title="show questions tagged &#39;ide&#39;" rel="tag">ide</a> should be split into <a href="https://arduino.stackexchange.com/questions/tagged/arduino-ide" class="post-tag" title="show questions tagged &#39;arduino-ide&#39;" rel="tag">arduino-ide</a> and individual tags such as <a href="https://arduino.stackexchange.com/questions/tagged/eclipse" class="post-tag" title="show questions tagged &#39;eclipse&#39;" rel="tag">eclipse</a></li>
</ul>

<hr>

<h2>Spelling</h2>

<p>These tags are mostly ones that need to be separated with a "-".</p>

<p>[None]</p>

<hr>

<h2>Synonyms</h2>

<p>Synonyms require significant reputation or moderator abilities to create. The "master tag" (or whatever the proper term is) will replace the synonym when typed.</p>

<ul>
<li><a href="https://arduino.stackexchange.com/questions/tagged/atmega328" class="post-tag" title="show questions tagged &#39;atmega328&#39;" rel="tag">atmega328</a> I don't know what to do about this one really but often people tag this along with <a href="https://arduino.stackexchange.com/questions/tagged/uno" class="post-tag" title="show questions tagged &#39;uno&#39;" rel="tag">uno</a>/<a href="https://arduino.stackexchange.com/questions/tagged/arduino-uno" class="post-tag" title="show questions tagged &#39;arduino-uno&#39;" rel="tag">arduino-uno</a></li>
<li><strike><a href="https://arduino.stackexchange.com/questions/tagged/build" class="post-tag" title="show questions tagged &#39;build&#39;" rel="tag">build</a> → <a href="https://arduino.stackexchange.com/questions/tagged/compile" class="post-tag" title="show questions tagged &#39;compile&#39;" rel="tag">compile</a> Some beginners may tag it as <a href="https://arduino.stackexchange.com/questions/tagged/build" class="post-tag" title="show questions tagged &#39;build&#39;" rel="tag">build</a> but for the <em>physical</em> construction of a project.</strike> Mods have decided to leave it and watch it.</li>
</ul>

<hr>

<h2>Tags to watch in the future...</h2>

<p>Tags for topics that may be deemed off-topic soon.</p>

<ul>
<li><a href="https://arduino.stackexchange.com/questions/tagged/enclosure" class="post-tag" title="show questions tagged &#39;enclosure&#39;" rel="tag">enclosure</a> Will we allow shopping questions here?</li>
</ul>
