Understanding -nct and -nt

I am trying to understand GATK's parameters for parallelism:

-nt / --num_threads controls the number of data threads sent to the processor

-nct / --num_cpu_threads_per_data_thread controls the number of CPU threads allocated to each data thread

So, is the following example true?

-nt 8 means you use 8 cores

-nct 8 means you use 8 threads within a single core

Thanks!