A placeholder is temporary example text that appears inside an empty input field. For example, a search box might show “Search products” before you type anything.
It gives a hint about what to enter, but it disappears when you start typing. That is why a placeholder should not be the only label: after it disappears, people still need to know what the field is for.
Use short, helpful examples, and keep the actual field label visible so the form remains understandable as someone fills it in.