<p><a href="https://stats.stackexchange.com/questions/tagged/kernel" class="post-tag" title="show questions tagged &#39;kernel&#39;" rel="tag">kernel</a> and <a href="https://stats.stackexchange.com/questions/tagged/kernel-trick" class="post-tag" title="show questions tagged &#39;kernel-trick&#39;" rel="tag">kernel-trick</a> are two different tags on CV, with the first one reserved for kernel smoothing and density estimating, and the second one for kernel trick in maching learning (kernel SVM, kernel PCA, etc.). I noticed that <em>a lot</em> of people confuse these tags, mostly by using <a href="https://stats.stackexchange.com/questions/tagged/kernel" class="post-tag" title="show questions tagged &#39;kernel&#39;" rel="tag">kernel</a> instead of more specific <a href="https://stats.stackexchange.com/questions/tagged/kernel-trick" class="post-tag" title="show questions tagged &#39;kernel-trick&#39;" rel="tag">kernel-trick</a>.</p>

<p>This is bad, because e.g. questions about kernel PCA are currently divided (approximately evenly) between these two tags. I see two possible solutions:</p>

<ol>
<li><p><a href="https://stats.stackexchange.com/questions/tagged/kernel-trick" class="post-tag" title="show questions tagged &#39;kernel-trick&#39;" rel="tag">kernel-trick</a> is removed as a separate tag and becomes a synonym of <a href="https://stats.stackexchange.com/questions/tagged/kernel" class="post-tag" title="show questions tagged &#39;kernel&#39;" rel="tag">kernel</a>.</p></li>
<li><p>The questions confusingly tagged should be re-tagged.</p></li>
</ol>

<p>Personally, I think that the tags are separated quite well and would therefore prefer the second option. Moreover, I was going to go ahead and re-tag all questions about kernel PCA to <a href="https://stats.stackexchange.com/questions/tagged/kernel-trick" class="post-tag" title="show questions tagged &#39;kernel-trick&#39;" rel="tag">kernel-trick</a> (and possibly some other questions about SVMs, if I come across any). This would, however, bump all these questions to the front page, and if I re-tag them in one sitting, then there will be lots of questions on the same topic edited by me appearing on the front page practically one after another.</p>

<p>Would this be okay?</p>

<p>[Of course, I can also make some other improving edits and maybe even answer some of these questions along the way, to make this less of a book-keeping activity. But still.]</p>

<p><strong>Update</strong></p>

<p>There are currently <a href="https://stats.stackexchange.com/questions/tagged/kernel+svm">68 questions</a> tagged with <a href="https://stats.stackexchange.com/questions/tagged/kernel" class="post-tag" title="show questions tagged &#39;kernel&#39;" rel="tag">kernel</a> and <a href="https://stats.stackexchange.com/questions/tagged/svm" class="post-tag" title="show questions tagged &#39;svm&#39;" rel="tag">svm</a> and <a href="https://stats.stackexchange.com/questions/tagged/kernel+pca">7 questions</a> tagged with <a href="https://stats.stackexchange.com/questions/tagged/kernel" class="post-tag" title="show questions tagged &#39;kernel&#39;" rel="tag">kernel</a> and <a href="https://stats.stackexchange.com/questions/tagged/pca" class="post-tag" title="show questions tagged &#39;pca&#39;" rel="tag">pca</a>. Whereas I was originally referring only to questions on kernel PCA, the problem seems to be much more severe in the SVM topic. For comparison, there are only <a href="https://stats.stackexchange.com/questions/tagged/kernel-trick+svm">16 questions</a> tagged with <a href="https://stats.stackexchange.com/questions/tagged/kernel-trick" class="post-tag" title="show questions tagged &#39;kernel-trick&#39;" rel="tag">kernel-trick</a> and <a href="https://stats.stackexchange.com/questions/tagged/svm" class="post-tag" title="show questions tagged &#39;svm&#39;" rel="tag">svm</a>.</p>

<p><strong>Update 2</strong></p>

<p>Turns out, this issue was discussed two years ago: <a href="https://stats.meta.stackexchange.com/questions/1115/what-does-the-kernel-tag-refer-to">What does the kernel tag refer to?</a> where @mbq and @whuber argued that <a href="https://stats.stackexchange.com/questions/tagged/kernel-trick" class="post-tag" title="show questions tagged &#39;kernel-trick&#39;" rel="tag">kernel-trick</a> is unnecessary. I think I am happy to accept this point of view, but that would mean that <a href="https://stats.stackexchange.com/questions/tagged/kernel-trick" class="post-tag" title="show questions tagged &#39;kernel-trick&#39;" rel="tag">kernel-trick</a> should be merged with <a href="https://stats.stackexchange.com/questions/tagged/kernel" class="post-tag" title="show questions tagged &#39;kernel&#39;" rel="tag">kernel</a>.</p>

<p><strong>Update 3</strong></p>

<p>I just realized that there exists <a href="https://stats.stackexchange.com/questions/tagged/kernel-density-estimate" class="post-tag" title="show questions tagged &#39;kernel-density-estimate&#39;" rel="tag">kernel-density-estimate</a> tag (used 45 times), which could most likely cover almost all uses of <a href="https://stats.stackexchange.com/questions/tagged/kernel" class="post-tag" title="show questions tagged &#39;kernel&#39;" rel="tag">kernel</a> tag that are not referring to kernel trick...</p>
