[brainyexpert]

Search Engine Optimization (SEO): aims to gain positioning in the natural listings, or as they also call it, organic listings. They are not other than the results that appear in the left column of the page. There is no cost to you when someone clicks on those results, but in return, SEO Optimization requires a lot of patience, investing time and being willing to wait.

Search Engine Marketing (SEM): These “sponsored links” are basically results over which the advertiser has control. Companies hire to place their ads on search results pages that match what they are offering. These links are usually right and top of the page. And if you are the advertiser, you must pay each time someone clicks on them, but the good thing is that you define in advance how much you are willing to pay. And the results basically act like an auction, making them appear above those offering pay more.