Search engine optimization (SEO) refers to practices, strategies, and processes for improving a website's online visibility on search engines such as Google, Bing, and Yahoo. 

There are two types of SEO: on-page and off-page SEO. On-page SEO focuses on optimizing parts of your website that are within your control. This includes optimizing your title tags and meta descriptions and writing in-depth, quality content. 

Meanwhile, off-page SEO focuses on increasing the authority of your domain. This is done by earning backlinks from external websites or sharing links across social media channels.