If you create a spreadsheet for a chart and skip some column or row labels, the
chart will default text in such as "row n" or "column n".

  A   B
1 Jan 123
2     456
3 Mar 789

With the above, the second bar in the chart will have a label of "Row 2".  Quite
often we skip row labels since with large amounts of data the labels get too
messy.  This happens with spreadsheets imported from excel (although in excel
they are blank) and with new spreadsheets created with OOo.  If you enter a
space in the row label it goes away, but I feel that requirement is poor because
a blank cell should be a blank cell without having to enter spaces.