The MAIN OBJECTIVE of SEO is by increasing the ranking of a website on a search engine, the traffic increases.
Increase in the number of visitors ultimately increases the product visibility. Higher product visibility directly reflects higher number of sales.
SEO is the practice of promoting a web site by increasing its position in search results on the major search engines. Those search engines comprise of Google mainly but also include Yahoo!, Bing, and a few others. The idea is to make the site appear higher in the list of search