Search engine optimization (SEO) is the process of increasing the quality and quantity of website traffic by increasing the visibility of a website or a web page to users of a web search engine. [Wikipedia]
There are a few key things to note here:
1) Purpose - The purpose is a continuous increase in the quality and the quantity of visitors to your site. You need more of the right visitors in order to improve your sales (or whatever the purpose of your website is)
2) Process - SEO is an ongoing exercise. Search Engine rules change, competition increases, targeted keywords change in popularity.
3) Users of a Web Search Engine - SEO is only one mechanism in the battle to attract the right visitors. Others include active marketing, word of mouth, social media, referrals, etc. But it is an important one, as most users will use a search engine if they are looking for a service or product from cold. There are many search engines, but the most popular is Google.
A recent study in 2019, listed the top 10 search engines as:
- Internet Archive