It is the process to optimize your website using various ways to generate traffic and improve your search engine ranking organically.
Search engine marketing uses paid search advertising to get ranked. SEO and SEM are two sides of a same coin.
Pay per click is an online advertising model. Here the advertiser pays a publisher every time when the advertisement link is being clicked.
Social media optimization is the use of different social media platforms to get more traffic and grow the online presence of your business.