An [abbreviation] sometimes used in [British] schools for "[Craft], [Design] and [Technology]".

It covers a wide range of topics such as

Metal work
Wood work
"Technology" - may involve building things out of metal or wood, but often computer-interfaced or more "cross-disciplinary"
"Graphics" - technical design and drawing
Sometimes the more traditional art lessons are also included under CDT (eg Painting and Drawing, Printing, Pottery etc)

The facilities needed to teach CDT can be quite expensive - decent [public school]s (which are private schools... never mind) may have multiple workshops with proper industrial [lathe]s, [milling] machines, drill-presses etc. There has also been a trend over the last 15 years to introduce [CAM] systems (Computer Aided Machining) - for example, a software package which allows you to design something that a lathe can make, and then send it straight to a computer controlled lathe which automates the entire process.

Many schools will also offer CDT courses to [GCSE] or [A-Levels].

CDT (thing)