After you have opened a screen in the Screen editor, right-clicked a solitary label on the screen (without associated entry field) and chose Properties in the pop-up menu, the Screen object properties window opens. On the Field conditions tab (meaning: Label conditions) in that window, you can set conditions under which the current label must be hidden from view.
Click here for information on how to edit screen object properties in general.
On the current tab you'll find the following settings:

The Copy button

If the Copy button is active, it means there's a hidden label condition in the pre-6.6.0 format present. Click the Copy button to convert it to the 6.6.0 (and higher) format and make it visible. A hidden condition doesn't work. If the Copy button is greyed out, it just means there never was any condition for this label.

Suppress & Read-only conditions

From Adlib 7.3, solitary labels may be conditionally hidden (the Read-only conditions do not apply to labels and can be ignored). This means that a label may be visible or not, dependent on the value(s) in certain  fields. This functionality is meant to be able to create more surveyable screens by only showing labels if an associated key field is filled in by the user. When a label is not visible during editing of a record as a consequence of a condition which you set here, then no strange empty spot will be present in the relevant screen, because all fields and labels underneath it will have moved one line up. And as soon as the label does become visible, the other fields will move back down again.

The conditions under which the current label must become/remain invisible must be specified in the upper box. Enter a single expression or a plural, Boolean expression as the condition in either or both boxes. Every time you open a record for display or editing, and every time you leave a field in edit mode, all relevant expressions will be evaluated. When this screen is associated with the current data source and if the suppress condition is true, the label will be hidden in the detailed display of a record, while if the result if false, the label will be shown. See the general topic Conditional screens and fields for a full description of this functionality and its possibilities.

The basic form of a single expression is:

<field or constant> <operator> <value>

Example of a suppress condition:

S6 = English && S7 = GBP

Result: the current label will be hidden if the tag S6 contains the value English and the tag S7 contains the value GBP.