SSL acceleration is a method of offloading the processor-intensive public-key encryption algorithms involved in SSL transactions to a hardware accelerator.
Typically this means having a separate card that plugs into a PCI slot in a computer that contains one or more co-processors able to handle much of the SSL processing.
SSL accelerators may use off the shelf CPUs, but most use custom ASICs and RISC chips to do most of the difficult computational work.
Read more about SSL Acceleration: How It Works, Vendors