Frequently it was asked by various people to distinguish between SEO and SEM and I think there is confusion about these terms. Though I am not expert in this field but whatever the information I have gathered SEM refers to the short text advertisment which usually appear at the top or bottom the right hand side of search engine. Generally it is called as "sponsored link/results" SEM generally referred as PPC(pay per click) advt because payment will be made only when some one click on the advt but not when advt is displayed. SEO is generally displayed on the left hand side of the page . SEM is an immediate gratification to advt media but SEO is a long term approach. If anybody is having more information about the subject can elaborate for the beneficial of the members.