See also: place holder
placeholder (plural placeholders)
- 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 is placeholder data, so you'll want to include the real numbers as soon as you have them.
2013 February 14, Scott Tobias, “A Good Day To Die Hard [film review]”, in The AV Club, archived from the original on 10 March 2016:
that which holds, denotes or reserves a place for something to come later