system — 2012-07-24T23:46:33-04:00 — #1
hawk — 2012-07-24T23:56:38-04:00 — #2
Search Engine Marketing
system — 2012-07-25T08:25:54-04:00 — #3
so SEM means Search Engine Marketing as it has been already told.
Also it is a process of gaining the upper position of a website to make it popular by using different keywords.