From MEPIS Documentation Wiki
SMP -- Symmetric Multiprocessing, is a multiprocessor computer architecture where two or more identical processors are connected to a single shared main memory. Most common multiprocessor systems today use an SMP architecture.
In order to take advantage of this feature you need to use a SMP enabled kernel. If you have an older version of MEPIS that does not, follow this howto to Install a new kernel that supports SMP.