HDML stands for Herp-Derp Markup Language. Broken or incorrectly implemented HTML that ends up being displayed as garbled text on the page, such as the following:
Show the one you love how you <i>really</i> feel this Christmas!
Show the one you love how you <i>really</i> feel this Christmas!
The frequent occurrence of HDML in the stranger's email body led Randolph Carter to suspect a phishing scheme.
by hypomnesis March 9, 2011