SEO, or Search Engine Optimization, is the process of optimizing your website to improve your ranking for specific keywords and key phrases on search engines like Google. SEO consists of many different factors such as:
Keyword optimization
Title tag and H1 optimization
Semantically related keywords
Meta descriptions
Keyword density
Internal links
Search intent
Content creation
Inbound links
Citations
Code optimization
User experience factors (i.e. time on site, bounce rate, etc.)
Without a proper SEO strategy in place it is extremely difficult for your website to rank predominately.