KVM (Kernel Virtual Machine) is a Linux kernel module that allows a user space program to utilize the hardware virtualization features of various processors. Today, it supports recent Intel and AMD processors (x86 and x86_64), PPC 440, PPC 970, S/390, ARM (Cortex A15, AArch64), and MIPS32 processors.
QEMU can make use of KVM when running a target architecture that is the same as the host architecture. For instance, when running qemu-system-x86 on an x86 compatible processor, you can take advantage of the KVM acceleration - giving you benefit for your host and your guest system.
The KVM project used to maintain a fork of QEMU called qemu-kvm. All feature differences have been merged into QEMU upstream and the development of the fork suspended.
To use KVM pass --enable-kvm to QEMU.