Here is an excerpt from the Help on the dot operator.
The . (dot) operator usually indicates that what follows is an item defined by Microsoft Access. For example, use the . (dot) operator to refer to a property of a form, report, or control.
Note You can also use the . (dot) operator to refer to a field value in an SQL statement, a Visual Basic for Applications method, or a collection. For example, the identifier Forms![Orders].Controls refers to the Controls collection of the Orders form. However, because the Controls collection is the default collection for forms and reports, it's usually not necessary to refer to it explicitly.