The form or report's Modal and PopUp properties are set to Yes.
The form or report is hidden.
The form or report opens minimized in the Windows taskbar.
(Default) The form or report opens in the mode set by its properties.
When opened from VBA, a form will open in Form View even if the form properties specify DataSheet view, unless an alternate view is specified.
“Like tourists huffing and puffing to reach the peak we forget the view on the way up” ~ Friedrich Nietzsche
Access Enumerations - MSDN
OpenForm - Open a form.