A whorish female. Land ho doesn't neccesarily mean they're large, fat, or whale-like, but it's a nice addition if they are fat. It's sorta like how to pass off calling a girl a whore in front of teachers without getting teachers pissed. You're supposed to scream it like when a sailor spots land.
Chick one: "Ugh, here she comes. I can't believe she's dating Monty. She knows I've liked him for, like, ever."