A VDT is the same as a VDU. VDT is an abbreviation for 'visual display terminal'.
[mainly US]
VDT in British English
computing
abbreviation for
visual display terminal
visual display terminal in British English
(ˈvɪʒʊəl dɪˈspleɪ ˈtɜːmɪnəl)
noun
another name for visual display unit
▶ USAGE The abbreviation for visual display terminal is VDT
visual display unit in British English
noun
computing
a device with a screen that displays characters or graphics representing data in a computer memory. It usually has a keyboard or light pen for the input of information or inquiries