  In this expository note we present an introduction to the Gabor wave front
set. As is often the case, this tool in microlocal analysis has been introduced
and reinvented in different forms which turn out to be equivalent or intimately
related. We provide a short review of the history of this notion and then focus
on some recent variations inspired by function spaces in time-frequency
analysis. Old and new results are presented, together with a number of concrete
examples and applications to the problem of propagation of singularities.
