An explicit label must be provided for each form field.
Note
If it is not practical to add a label for each field (lack of space in the mock-up, for example), there are other solutions that can be used later in the development phase (adding tooltips, for example). Nevertheless, this is a compromise solution that is less effective than directly optimizing the form field label.
Examples
In this example, the “Search” and “Language” form fields both have explicit labels.
In this example, a label has been added to the field for the second line of the address.