Every Access database has a setting for Overlapping /Tabbed Windows which can be set under Options ➞ Current Database ➞ Document Window Options.
Overlapping Windows = Default in Access 1.0 to Access 2003
Tabbed Windows = Default in Access 2007 +
The Tabbed/Overlapping option affects all database objects: Tables, Forms, Reports, Macros, Modules etc
In Access 2016 on Windows 10 Overlapping Windows have a 1 pixel border which makes resizing document windows very difficult.
This has been fixed in Office 365.
Tabbed windows should not be confused with the Tab control which provides very similar functionality when stretched to fill an entire form.
In a database with Overlapping Windows a form with the Popup property set to TRUE will behave just like any other form but will always sit on top of other forms.
In a database with Tabbed Windows a form with the Popup property set to TRUE will (when in Form view) break out of the tabbed interface and appear like an overlapping window.
Although popup forms can be useful for grabbing the users attention, you may prefer to disable their maximise and minimise buttons.
“The biggest tab the public picks up for fossil fuels has to do with what economists call 'external costs,'
like the health effects of air and water pollution” ~ Jeff Goodell
Related:
Defaults - How to set form default properties.
Access Form References - Reference the controls on other forms or subforms.