A single-column index is a named or unnamed index containing one column only. A single-column indexed column is a column on which a single-column index was created.
A multiple-column index is a named index containing various columns. A multiple-column indexed column is a column which is an element of one multiple-column index at least.
An index list is a list of keys belonging to an index. The following is true for every index column: All table rows with keys which are specified in the list contain the same value in this column.