Search Engine Optimization refers to the collection of techniques and practices that allow a site to get more traffic from search engines (Google, Yahoo, Bing). SEO can be divided into two main areas: off-page SEO (work that takes place separate from the website) and on-page SEO (website changes to make your website rank better).
Without Search Engine Optimization, there is no way that internet users or customers can find your website, unless you choose to advertise offline like using radio, TV or print media. But even though you go for offline advertising, you are hitting a broad audience but not the specifically targeted to your products or services, besides which, not all of them use the internet or are even looking for your services.
The most effective way to get long lasting success is to ensure your website appears on the first page of the SERPs (Search Engine Results Pages) for specific keywords and phrases that you want to appear for. This is how you ensure that a Targeted Internet User finds your website and becomes a potential customer or user of your service.