For the purposes of this Chapter—
(a)a council is “subject to a scheme for whole-council elections” if all of its councillors are to be elected in each year in which it holds ordinary elections of councillors;
(b)a council is “subject to a scheme for elections by halves” if one-half (or as nearly as may be) of its councillors are to be elected in each year in which it holds ordinary elections of councillors;
(c)a council is “subject to a scheme for elections by thirds” if one-third (or as nearly as may be) of its councillors are to be elected in each year in which it holds ordinary elections of councillors.