The major search engines that you’re probably familiar with today were created from 1993. Some of them are below:
AltaVista — 1995
Ask Jeeves — 1997
To understand what SEO is, we should first know about Search Engines. When you type a word or phrase into a search box of any search engine and click a button. Within a few seconds, you will see thousands of pages will appear. Then all you have to do is click through those results to find what you want. There is an agent which looks every URL on the web page and collects the information like keywords and phrases on each page of the website in its database. This agent is so called, a crawler, spider, or robot.
Search Engines are classified into three categories:
1) Primary Search Engines – There are three major search engines like Google, Yahoo and MSN. These are called primary search engines. These three create maximum traffic for your website and our all SEO will focus on these three search engines.
2) Secondary Search Engines – The search engines like Lycos, LookSmart, Miva, Ask.com, and Espotting are called secondary search engines. They are useful only for regional and narrowly focused searches. They don’t generate as much traffic as the primary search engines.
3) Targeted Search Engines - These search engines are very narrowly focused to a general topic. Examples of targeted search engines include CitySearch, Yahoo! Travel and like other types of search engines whose ranking criteria vary from one search engine to another.
SEO is not as easier as you understand. It’s a continuous effort. A mildly change can affect your search engine ranking. SEO is a holistic approach to improving your search engine rankings. As such, it requires attention to your whole site. So I recommend you that after the initial implementation of SEO during the building of website you should do proper SEO daily in your routine time.