title: Pop up text box
body: <p>I'd like to know how is called the box that pops up and overlays on top of a webpage.</p>
  
  <p>Examples are: 
  Facebook photos - It grays the background webpage and opens a separate pop up to view pictures.</p>
  
  <p>Advertisements - The box that you (often) have to click the 'x' to get out.</p>
  
  <p>Basically it is on the same page but it shows up in the middle, on top of your main webpage for critical information or not. </p>
  
  <p>I'd like to create one to explain what the webpage is supposed to be about, sort of an orientation, or when a person requests it; for example, by clicking "learn more".</p>