The optimum temperature or in some cases, range of temperatures at which a tea is best consumed.
Hot enough to warm the mind, body and soul, yet not too hot to scald the tongue and spoil the taste of accompanying biscuits.
PDT is very personal, the actual temperature will vary from person to person.
Warning: Once tea hits PDT, you usually have less than three minutes to consume before tea hits a suboptimal temperature. This of course depends on the drinking vessel used.
Cornelius: Hey Reginald, why do you have a thermometer and an air conditioning unit in your tea cup?
Reginald: Gotta get that shit down to PDT bro.
Dude 2 "Yeah it definitely says PDT so find a new hobby"