Определение placeholder в Английский Язык Английский Язык словарь
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.
{i} symbol in an expression that can be replaced by the name of any element in a set; person holding a government position (Mathematics)