What is a TERF, and why does it matter in today's political climate?

After several years of fighting behind the scenes, largely ignored by politicians and media outlets that have steadfastly shut their eyes to the fact that there is a leftist feminist critique of “gender identity,” TERFs finally have entered the public debate about whether there is such a thing as “gender identity” and whether it deserves the same legal protections as those granted to biological sex.

But what is a TERF? I want to clear up some misconceptions about what the term means and about who we actually are as a political movement.