I have just dowloaded Mma 11.3 with a trial licence. In the download page you can see:
That I can use 2 controlling kernels and 4 computing kernels.
What is the difference between controlling and computational kernels?
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In practice, the number of "controlling kernels" means how many instances of Mathematica you can run.
"Computing kernels" is how many subkernels may run when using
Parallel... operations, i.e. how many CPU cores you can make use of.
Here's the explanation from Wolfram: