Unless I am wrong, it is when someone is born looking like one or both genders, but still has the parts of both genders.
There's a character like this in an episode of Call the Midwife
I FIND SOME FUNNY, WHOLESOME, AND/OR RELATABLE MEMES TO UPVOTE; I GO TO THE LGBTQ STREAM; I NOTICE A LACK OF INTERSEX MEMES; I NOTICE A LACK OF INTERSEX MEMES; I WANT TO CHANGE THAT!