My first instinct of L2 refers to the CPU cache. I don't think you can change or alter the L2 cache for newer CPUs though. Not sure.
As far as what L2 cache mean, it's like memory that is outside of the processor chip. It uses static RAM which are expensive to produce and by keeping frequently used information from programs in cache, the computer avoids accessing the slower main memory (DRAM). So it speeds up the process that way.
*Fact: Microsoft Window's Blue Screen of Death vs Computerforums.org's White Screen of Death. Which is worse?