placeholder

noun

1. Something used or included temporarily or as a substitute for something that is not known or must remain generic; that which holds, denotes or reserves a place for something to come later.

   “This data is a placeholder, so you'll want to include the real numbers as soon as you have them.”

   “As the years go by, speech reverts to childhood levels of disfluency, with more pauses, more errors, more repeated words, but even the peak years are not great: up to 8 percent of the average person’s word output consists of meaningless fillers and placeholders like um, uh and er.”

   “"I'm on vacation," [Bruce] Willis grumbles several times throughout A Good Day To Die Hard, in what counts as the film's sole running joke, a lame placeholder until he arrives at the big "yippee-ki-yay" punchline.”

2. A non-editable caption initially displayed in a blank text box to indicate its function.