pop-up
noun /ˈpɒp ʌp/
  /ˈpɑːp ʌp/
 [only before noun]- a computer menu, window, etc. that can be brought to the screen quickly while you are working on another document; a computer window, especially one containing an advertisement, that appears on the screen although it has not been requested- an advertising pop-up
 
- a shop, restaurant, etc. that opens quickly somewhere and is designed to only use that location for a short period of time- The designers opened a pop-up in the main shopping area as part of the fashion event.
 
- (also pop fly)(in baseball) a ball that is hit high into the air but does not go far, making it easy to catch