What does the K stand for at the end of an Intel CPU model number?

With Intel CPUs you may notice that some models have two options available but one will have a K at the end, such as the 3770 and the 3770K.

The difference is simple, if the processors model number has a K at the end then that tells us that the CPU has an unlocked multiplier, this means that overclocking the CPU is much much easier.