What is SEO?
Google defines SEO (search engine optimization) as follows:
“Improving a website’s presence in organic search engine results.” online marketing vocabulary, Learn with Google
It seems like a very simple definition, but let us elaborate more on this. Basically, it is the process of improving the visibility of your website to your online audience via search engines. In other words, optimization methods which help improve your website’s ability to be listed on the first or second page of organic search results.
In the most simplest terms, you want to create unique, fresh, quality content written for your audience and then you want to build quality links from relevant websites to point to that specific content. Of course, SEO involves a lot of work and there have been many books written about it, but if you stick to the basic rules of writing quality content and building quality links, then you are taking the right steps towards improving your website’s presence in organic search results.
Read about: How to SEO, Fundamentals and more

SEO Stand for search engine optimization
SEM stand for the Search engine Marketing
SMO stand for social Media Optimization

SEO stand for search engine optimization and SMO stand for social media optimization. both are different in many ways.

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SEO Stand for search engine optimization
SEM stand for the Search engine Marketing
SMO stand for social Media Optimization
They all are Part of Digital Marketing.