Not sure what it is called

Okay have been away from things for a while. I want to be able to point to an area on an image that when ia mouse goes over the area a non persistant display is shown of the text on the picture. The main picture is an large timeline that if I do an enlarged image it isn't really best for people to be able to read the text. I know there is a map for image.that can create a popup with a new browser window. Since there are 9 columns I really don't want to go that way, but could. Doing a popup message is again a situation where people have to click to close the popup. Plus people block popups. What I would like is something like the image below. When you roll over the GitHub hyperlink a preview of the page is displayed. That isn't what I want, but it is the look I want. When you move the mouse the display goes away. So again 1 need 1: when mouse over an area of an image want a message either typed material or a small image is displayed. So a onMouseOver event 2. Then on exit the display goes away with user doing nothing but moving mouse. onMouseOut event 3. A non modal display without buttons or border. 4. Something that doesn't make the user have to have popups allowed. 5. A picture with many many areas going to an different "popup". So the question. What is what I want to do called? What is the easiest and less impact on the site size. Thank you. I have attached an image that I am looking at, but not associated with a link.