Periodization in detail is THE most effective philosophy of strength training ever conceived. As Dswithers stated above, it goes by 'periods' of training. Periodization is broken down to and also what is called a "Macrocycle" (the entire training cycle).. as trianing progresses and you begin to make gains, your Macrocylce is then devided into "Mesocycles", a time period of 2-6 weeks. Meso's are further broken down into Microcylces, which defines each individual workout. Basically, keeping a good record of your entire Macrocycle, and all it involves will keep (or get you there) your body in PEAK physical condition.
Hope that made sense?