Rotation of directors
A number of directors normally retire each year and offer themselves for re-election (the number or proportion is usually stated in the Articles of Association). This is to give shareholders an opportunity of changing the directors without going through the procedure necessary to dismiss them. Table A as at present constituted requires that at a company’s first annual general meeting all directors retire and at subsequent annual general meetings one-third of them do.
Reference: The Penguin Business Dictionary , 3rd edt.