Placeholders are essential tools that designate a space for future content. They are commonly used in website design, graphic design, and computer programming. Some common synonyms for placeholders are "blanks," "dummy text," "placeholders text," "filler," "markers," "pretext," and "stand-ins." The term "mock-up" often implies the use of a more detailed image or object, while "prototype" may suggest a more fully developed concept. Dummy data is another term which is sometimes used in computer programming to describe a sample dataset that is not intended for actual use. Whatever terminology you use, placeholders remain a crucial part of efficient design and programming.