SEO means Search Engine Optimization. It is used to get traffic from various sources like free, organic, editorial and can be natural listings on different search engines.

There are many different search engines that are very popular have such results where various sites and other things such as other content, videos or local listings ar displayed and are considered to different internet users on the basis of their ranks. Since there paid search
ads so there is no payment.
Like this way there are organizations which provide seo services. Among them very popular is swaastik

For more details