PTG stands for Pretty Tall Girl. This distinction needs to be made because a short guy, say around 5'7-5'10, who says he likes tall girls is probably not talking about girls the same height as him. However, you'll always find some girl within the same height range
going on about how tall she is. Therefore, when talking about girls that are actually tall (6'+) we use the word PTG to distinguish them from TTGs (
Technically Tall Girls).
It also works as a
double entendre. Pretty Tall Girl refers to the fact that they are pretty tall, but also to the fact they are pretty AND tall. This term should be used instead of BBW, because BBW is for fat women. Also it sounds a lot nicer than Giantess or Amazon, especially when you say the full word.