I think you mean “Combined Test”, not “Combined Training”
A “Combined Test” is a competition with a Dressage phase and a Show Jumping Phase. You combine the scores (using Eventing scoring) for your final result.
“Combined Training” is the old name for the sport that was also called “Three Day Eventing”, and is now called “Eventing”, with THREE phases: Dressage, Cross Country, and Show Jumpimg. The oranization that is now called “US Eventing Association” (USEA) was founded as “US Combined Training Association” (USCTA), and was called USCTA for over 40 years.