Most of the marketers agree that the primary categories under digital marketing are: Search Engine Optimization (SEO), Search Engine Marketing or Pay per click (SEM or PPC), Social Media Marketing (SMO or SMM), Content Marketing, Email, SMS / Whatsapp Marketing and Mobile Marketing, Marketing Analytics, Affiliate/Partnership Marketing and Content Marketing.
Digital marketing can be described as a variety of marketing strategies and technologies that are used online to reach consumers. It is a type of online marketing that allows companies to create a brand identity.
Search Engine Optimization (SEO).
Although it sounds like you are optimizing the search engine, but in fact it is the process of improving your site to increase its visibility when people search for products or services related to your business in Google, Bing, and other search engines.
SEO's main goal is to make a business rank higher in Google search results (SERPs). This will ultimately increase search engine traffic to their website. SEO marketers use keywords and phrases that consumers search online to achieve this goal.
According to wikipedia, Pay-per-click is an internet advertising model used to drive traffic to websites, in which an advertiser pays a publisher when the ad is clicked. Pay-per-click is commonly associated with first-tier search engines.