SEO (Search Engine Optimisation) is the practice of increasing the quantity and quality of traffic to your website through organic search engine results. Your website should be more than a brochure! It should augment your sales and marketing efforts. To do this, it needs traffic!
Off-site SEO (also called “off-page”) refers to actions taken outside of your own website to impact your rankings with search engine results pages. This can include things such as link building and is accomplished by other websites which promote your website through links.
On-site SEO (also known as on-page) is the practice of optimising elements on a website in order to rank higher and earn more relevant traffic from search engines. On-site refers to optimising both the content and HTML source code of a page. The ultimate goal of on-site can be thought of as making it as easy as possible for search engines and users to identify and understand a web page.