School closures, moving schools and inset days are all instances where a pupil might not be required to attend school, where other pupils might still be required to attend.
Cau ysgolion, symud ysgol, diwrnodau HMS, ac ati... yn achosion lle nad oes angen i ddisgybl fynychu'r ysgol o bosibl, tra bod disgyblion eraill yn dal i fod yn bresennol.