Default
The box is left unchecked. Checked
An action or item is selected. Disabled
The checkbox is inactive due to previously checked or unchecked boxes. Checked & disabled
An action or item has been pre-selected due to previously checked or unchecked boxes. Indeterminate
If all subordinate boxes are checked, the "mother checkbox" may be as well. But if only _some_ of them are, it's state is indeterminate, i.e. partially checked. This may come in handy if you work with nested checkboxes. Indeterminate & disabled
The box is indeterminate and can not be interacted with directly, but only via checking all of the subordinate boxes nested below.