explaining what is 180 and 360 requires a lot of writing but i will try to keep it simple.
180 where your appariased by your superior. or you are appraised by your boss, the person who is one level above you.
360 is where you are appraised by all parties. this includes your superior, your sub ordinates, your peers. basically your reviewed by people you tend to interact in an organization. these days software programs have been developed to help the HR people in dealing with 360 appraisal.
you might be familiar with 540 appraisal where the customer is also involved in appraising you.
26th April 2006 From Sri Lanka
27th May 2008 From India, Delhi