[OK]

The OK button executes the Apply button to accept your changes and then closes the Dialog. If the Dialog is connected to a command that does something, the command is executed after clicking OK.

[Apply]

This button accepts the changes you have made in the Dialog. After clicking Apply you can continue changing preferences in the dialog.

When Apply is located with OK and Cancel at the bottom of the dialog, does not execute the command. Instead, it simply updates your changes to some form of permanent storage like a parameter file.

[Cancel]

[Close]

These buttons close the dialog window without updating your changes since the last time you clicked Apply.

[Show >>]

[<< Hide]

These buttons enlarge or reduce the size of a Drop Dialog.