A Sconcha is a girl who is a mixture of the worst kind of woman. She is a slut, a whore, a bitch, easy, and a scumbag. Most girls who are called a Sconcha are the ones who are known for getting around. Not so much because they have a lot of actual sex, but because they go to random parties and goes down on guys that they have never met.
Usually you kind find a Sconcha in your family. The way you can usually detect one is the girl who is extrememly friendly to the males in her family. Although its very disgusting, this is usually the case.