What means "ref=hexometer"?

Read this if you noticed Hexometer in your website statistics.

Hexometer is a Website Health and Performance Monitoring Solution that reports crucial performance metrics. The website also offers Free Website Audit tools. Hexometer's Bot (also known as a web robot) reads the particular page(s) to analyze data then generates the requested reports.

For example if you scan a website by Tech Stack Checker Tool at https://hexometer.com/stack-checker then you will notice ref=hexometer in traffic analytics reports.