<p>This is mostly a question of how categorical variables should be encoded.  (The 'dummy variable trap' is simply that there is perfect multicollinearity if you use a separate dummy code for every level of a categorical predictor when there is an intercept in the model; see my answer at: <a href="https://stats.stackexchange.com/a/70700/7290">Qualitative variable coding in regression leads to “singularities”</a>.)  As such, we have a relevant tag already: <a href="https://stats.stackexchange.com/questions/tagged/categorical-encoding" class="post-tag" title="show questions tagged &#39;categorical-encoding&#39;" rel="tag">categorical-encoding</a>, although it's also related to <a href="https://stats.stackexchange.com/questions/tagged/multicollinearity" class="post-tag" title="show questions tagged &#39;multicollinearity&#39;" rel="tag">multicollinearity</a>. What might be helpful is to make a <code>[dummy-variable-trap]</code> tag &amp; make it a synonym of <code>[categorical-encoding]</code>.</p>
