Some use the term pop-up, but that has a negative connotation. And Wisepops aren't really pop-ups; those happen in a new browser window. Wisepops occurs in the same window and cause the webpage to be grayed-out will the overlay/light-box is on top.
Thus I prefer using the term overlay or light-box.
Wisepops has many uses, is easy to use, deploy on your website, and link to your ESP (email service provider).