placeholder

noun
1
a symbol or piece of text that temporarily replaces something that is missing
جای‌گزین, متن موقت, پرکننده, نشانه موقت, جای‌گیر
2
an item which is necessary in a sentence, but does not have real meaning, for example the word ‘it’ in ‘It’s a shame she left.’
پُرکننده, جای‌نگهدار