Content (Text) is the most significant part in the webpage to rank in search engines. If you want to get higher ranking with keywords in serp then use content or text in high quantity so that search engine could provide weightage to web pages on behalf. so, code to text ratio term is relates to content or text in the web page. code to text ratio is measurement of text and code presence in a web page separately and search engine use it to calculate percentage of text and determine relevancy of text in the web page. The higher text are available in the web page, higher ranking you can get in search engine.