Welding Operations is from start (cleaning, preheat) to actual welding using a welding process or processes (interpass temperature, cleaning (if applicable) and the completion of welding (cooling or after PWHT).

OP, there are several codes or specs that define welding operations. In my company, we perform a significant amount of structural welding, which is controlled by AWS D1.1. Have a look at AWS' website for more information. You can find several free resources on the internet for welding operations and what is contained in them, however, @metengr defined it pretty well in his response. Hope this helps.