Sabbatical Officers are normally elected annually, for a year term. Some student unions allow their sabbatical officers stand for re-election for a second year.
Sabbaticals are either taken in between studying (so between years two and three of a three year course) or after graduation. They are paid positions, generally by the University, and the officer is generally given student status for the year they are on sabbatical.
A University students' union will generally have between three and seven sabbatical officers - each with a specific job title and description. An example would be the President of the students union, or the Education and Welfare Officer.