Not long ago--say, twenty or even fifteen years ago--almost anybody would have defined such a school (which were still called "girls' colleges" when I was in elementary school) as one that admitted only students whose birth certificates identified them as female. And, I believe, very few people would have questioned such a definition or the policies derived from it.
Over the past few years, that's been changing. Actually, most women's schools did not have clearly-articulated policies about gender, except to say that those who are born male are not eligible for admissions.
A number of trans men have attended those schools. Most lived as female during their days in those schools; a few transitioned to male and the schools, to their credit, usually did what they could to support those men. However, as more than one official is quick to point out, such a policy is not an endorsement of the mistaken notion that trans men are "really" women.
Still, until last year, none of the country's female-only schools was willing to admit someone who identifies as female but was born as male. Mills College, in Oakland, CA, was the first to do so and to craft a "welcoming" policy for transgender women. Mount Holyoke College soon followed.
Now Smith College has done likewise. In doing so, the Massachusetts liberal-arts college has become the first "Seven Sisters" school to say it will consider applications from transgender women. The move came after the school came under heavy criticism--and threats of withheld donations from alumnae--after it denied the application of Calliope Wong, a trans woman from Connecticut. To be fair, when Ms. Wong applied, she was not yet legally recognized as female in her home state of Connecticut. Still, she was--and is--living as a woman, and her situation generated a petition that gathered over 4000 signatures.
How long before the other Seven Sisters colleges--and other single-sex schools--follow the lead of Mills, Mount Holyoke and Smith?