Public relations and advertment

PR is actually a kind of PROPAGANDA(宣傳), properly used by Nazi Germany and Communist China, for example. (But no one in a modern, democratic society likes the word propaganda)

we can also take it as the ART of building up a good image for a company (or the organization, the government etc. that we work for) among the general public, hoping that the people will support us in return (through buying our company's products or voting for our candidate in election)

advertisement (廣告) is the end product, i think. advertising (廣告制作) is the art of making advertisement. so advertising is ONE WAY the PR officers will take, but clearly being a good PR officer has to do much more than simply advertise something. (e.g. need to say something in press conference; promise the public that the company will improve in certain ways etc.)

2006-11-10 14:29:11 補充：
or we can say: PR is sometimes to promote ourselves in a HIDDEN way, and AD is done in a straight forward way through the media.