SEO done properly, by real experts with an outstanding track-record.
Search Engine Optimisation (SEO) is the process of optimising your website to achieve high natural listings within Google, Bing and Yahoo.
SEO is the process of continually improving your site to help it perform well organically in the search engines. The end goal is to increase organic traffic and, ulitimately, conversion numbers (whether that be sales, enquiries, or anything else).
The most common misconception about SEO is that it is all about ranking for a few core terms. Whilst these may help in pushing traffic to the site, it's more than likely that these selected terms are only driving less than 10% of your site's potential organic traffic, even if the site is performing well for them. Focusing on these rankings as a KPI means that you are effectively ignoring the remaining traffic, and most likely 1000s of other terms that your site could be targeting (if not more).