You can check the GMP bylaws for specific definitions. In layman's terms, the critical process, as the name implies, is the process that has a great impact on the quality of the product; the special process is the process that can not be judged by subsequent testing to be qualified.
To recognize the two, it is important to understand the purpose of the process or procedure and its effect on the product.
Example: soldering, this process has a different role for different products. Circuit boards for physical therapy equipment is mainly conductive, and conductive can be measured by a multimeter, this time welding is not a special process, is a key process. Oxygen generator cylinders, welding is mainly used in airtightness and strength, and strength can not be through the late economic test, then the process needs to be verified, this time welding is a special process.