placeholders >> /ˈpleɪshəʊldə/
Definition: [noun] A significant zero in the decimal representation of a number.
Example: The use of zero as a placeholder was probably first developed by the Babylonians, possibly as early as 1500 BCE.
Definition: [noun] An element of a sentence that is required by syntactic constraints but carries little or no semantic information, for example the word it as a subject in it is a pity that she left, where the true subject is that she left.
Example: According to this model, readers process text in parallel at several levels of analysis, which mesh the ease of identification with the role of function words as structural placeholders.