To be honest, I was not even aware of the term "dummy variable trap" until a few days ago, but it seems like the term is popping up more and more frequently at CV (note chonological ordering).
Do we need a tag for this? Maybe look for a canonical answer (e.g., this one, though it goes into many other aspects of collinearity besides the "trap")?
[dummy-variable-trap]
tag & make it a synonym of[ce]
. $\endgroup$