Hello,
The PRINTF macro is declared for the printf function. I would recommend to take a look at the trustzone example helloworld which is an example that has the non-secure part and the secure part.
In the secure part in order to print in the serial console it uses the PRINTF. To call the same function from the non-secure part it calls the NSE_PRINTF.
This function is defined in the veneer table which creates a non secure entry to use the printf function.
As shown below:

Best Regards,
Sabina