Hi Leon, from a Google search:
A polar orbit is an orbit where the satellite travels in a North to South direction instead of the common West to East orbit.
Because the earth spins in an Easterly direction, a polar orbit will eventually cover every possible combination of latitude and longitude.
This makes polar orbits very useful for satellites which monitor the earth, such as weather satellites and geographical survey satellites.
Cheers
Dennis
PS – See also:
http://www-spof.gsfc.nasa.gov/Education/wlopolar.html