vdimm - voltage of the RAM memory modules, usually tweaked by overclockers to achieve higher speed and performance
i7 - the brand name of the new Intel microprocessors. The microarchitecture of this new generation of processors has the memory controller built into the processor.
the "Core i7 vdimm issue" talks about the fact that the voltage of the RAM modules cannot (and should not) be tweaked independently of the CPU voltage (vcore). Otherwise if the vdimm is raised too high and the RAM is "fried" the CPU will be "fried" too. This was not the case in previous microarchitectures because the memory controller was NOT built into the CPU itself.