(Handheld Device Markup Language) A specialized version of HTML designed to enable wireless pagers, cellphones and other handheld devices to obtain information from Web pages. HDML was developed by Phone.com (now Openwave Systems) before the WAP specification was standardized. It is a subset of WAP with some features that were not included in WAP. AT&T Wireless launched the first HDML-based service in 1996. See WAP.