Mythdhr sounds like a rather odd and perhaps even random name for an official website. However, things become clearer upon closer inspection. The website is called my-THD-HR. Going further, that means – my The Home Depot HR.
And yes, that is the name of the employee self-service portal of The Home Depot. Employees and associates of THD can use mythdhr.com as a way to access several features and information about their job.