What does ACPI x86-based PC stand for?

ACPI or Advanced Configuration and Power Interface, is a specification that defines recognition for hardware, motherboards and other devices. It replaces the older AMP standard.

x86 is just referring to the processor. Its all based of x86 technology back from the IBM 8086 Cpu's. that's why for a while CPU's kept getting designated 286, 386, 486 etc. cause it was all based of the x86 technology