In the early 1990s, the word 'out' came to be used as a verb. 'To out someone' meant to tell the world that the person was a homosexual, usually a public figure. It was short for 'coming out of the closet', 'out of your cupboard', 'out of your house'.
It then developed. People who do the 'outing', who tell the world about the people, are 'outers'.
And then, people have been 'outed'. So, all kind of other usages developed. Gay rights activists took up the word. And now there are several websites with 'out' in the title.
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