<p>Somebody has just created <a href="https://stats.stackexchange.com/questions/tagged/correlation-matrix" class="post-tag" title="show questions tagged &#39;correlation-matrix&#39;" rel="tag">correlation-matrix</a> tag by posting this  question: <a href="https://stats.stackexchange.com/questions/182875">Is every correlation matrix positive definite?</a> Previously this tag did not exist, but of course there is well over a hundred older threads that could in principle be meaningfully tagged with it. I wonder if it is a good tag to have around, and if so, whether it should be slowly "propagated backwards".</p>

<p>Note that we do have <a href="https://stats.stackexchange.com/questions/tagged/covariance" class="post-tag" title="show questions tagged &#39;covariance&#39;" rel="tag">covariance</a> and <a href="https://stats.stackexchange.com/questions/tagged/covariance-matrix" class="post-tag" title="show questions tagged &#39;covariance-matrix&#39;" rel="tag">covariance-matrix</a>, but only used to have <a href="https://stats.stackexchange.com/questions/tagged/correlation" class="post-tag" title="show questions tagged &#39;correlation&#39;" rel="tag">correlation</a> until now.</p>
