The groove clearance is the proportion of the width of the installation groove of an O-ring that remains free after it has been pressed. The groove clearance is essentially dependent on two parameters.
While the groove width limits the available space, the cross-section and the compression (and thus the elliptical deformation) of the O-ring determine how much of this space remains free. When designing a seal, the groove width is selected so that there is sufficient groove clearance when the seal is pressed.