SEO stands for Search Engine Optimization, which is part of of digital marketing. SEO means to rank your website in the top of Google search result page. This can be done through on-page optimization and off-page optimization
SEM is another firm in digital marketing. Search Engine Marketing also known as Pay Per Click (PPC), that involves the promotion of websites by increasing their visibility in search engine results pages (SERPs) primarily through paid advertising.
Social Media Marketing(SMM) is a type of internet marketing which uses the benefits of social networking sites as a tool of promoting websites, thus increasing traffic towards them and learning from user’s direct reactions.