A skeleton screen shows pale shapes where content will appear while a page is loading. It is like seeing the outline of a place setting before the meal arrives.
For example, gray bars may stand in for a title and paragraph while an article is being fetched. This gives a clue about the page layout and can make waiting feel less abrupt.
Replace the placeholders as soon as the real content is ready. They should resemble the shape of what is coming, not pretend that information has already loaded. A simple loading message may be clearer for very short waits.