(1) A 32-bit x86 CPU. Since 1981, the x86 designation has referred to all sizes of x86 CPUs (see definition #2 below). However, as 64-bit x86 CPUs become more common, "x86" increasingly refers to 32-bit x86 CPUs, and "x64" refers to 64-bit x86 CPUs. See Intel 64 and Program Files.|
(2) Refers to the Intel x86 family of CPU chips, which includes the Core, Pentium and preceding models such as the 486 and 386. x86-based computers, including machines with x86-compatible CPUs from AMD and others, make up the world's largest hardware platform. See x86 compatible and x86 chip platform.
The x86 designation comes from the 8088, which was the first Intel CPU used in the IBM PC in 1981. The 8088 was a slower version of the 8086, which begat the 80186, 80286, 386 and 486, hence the "x" and the "86." The 486 was followed by the Pentium and its many versions and the Core line, but the x86 designation is still used. See 8088, Pentium, Intel Core and x64.