pop-up

Short definition from Wiktionary

Adjective

1. 1
   Coming into view suddenly from a concealed position.
2. 2
   Opening out to form a three-dimensional structure when the page of a book is opened.
3. 3
   Operating or existing for a brief period only; temporary.
4. 4
   Employing the cold launch technique.

Noun

1. 1
   A pop-up advertisement; an advertisement that is triggered to appear on a computer screen when the user accesses a particular web page.
2. 2
   A pop-up ball: a ball that has been hit to a considerable height above the infield or the shallow outfield; a pop fly.
3. 3
   A folded paper element which pops up from a book, greeting card, etc.
4. 4
   A business that opens for a brief temporary period only, such as a temporary restaurant.

Verb

1. 1
   To come up with a "pop" sound.
2. 2
   To appear without warning.
3. 3
   (Of an alert, advertisement, etc.) To suddenly appear onscreen.
4. 4
   To display as an alert, advertisement, etc. that suddenly appears on screen.