The term "window" is used with many different processes (not just manufacturing) to mean the range of parameter variation that produces an acceptable result or product. The parameters could be physical like temperature or temporal in nature. For example, a launch window is selected based on timing the rotation of the earth and other factors with achieving a desired orbit or intercept course with a satellite. This allows the launch organization to complete their mission with a minimum expenditure of resources, such as time, money, fuel, staffing, etc.
A large process window would be controlling the temperature and humidity of a clean room at 65-75 F (70+/-5) and 35-45 %RH (40+/-5).
A small process window would be controlling the same room at 68-72 F (70+/-2) and 38-42 %RH (40+/-2).
It's easy to see that the smaller process window has tighter acceptable tolerances.
xnuke
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.