For question directly about programming 'system-on-chip' or writing 'hardware description language' code for these systems.
A 'system-on-chip' is just as the name says. The entire (or almost) system is on a single chip. Mass storage and RAM maybe separate or integrated. Use the tag for question directly related to a 'system-on-chip' and not just because your issue is incidentally occurring on such a platform.
See: System-on-Chip at Wikipedia.
Related: embedded, embedded-linux, vhdl, verilog
Do not use the tag soc, it is very ambiguous.