Introduction:
The McCall quality model is a framework that helps in assessing and measuring software quality. It consists of three levels of quality attributes: product operation, product revision, and product transition. Each level is further divided into several quality factors. The second level, known as product revision, includes quality criteria as its quality factors.

Explanation:
The second level of quality attributes in the McCall quality model is termed as product revision. This level focuses on the internal characteristics of the software that contribute to its overall quality. It deals with the software's maintainability, flexibility, testability, and other factors that make it easier to revise and improve.

The quality factors at the product revision level are further divided into quality criteria. Quality criteria are specific attributes or characteristics that are used to assess the quality of the software. These criteria provide guidelines and specifications for evaluating the software's performance in terms of the defined quality factors.

Example:
To illustrate, let's consider the quality factor of maintainability at the product revision level. Maintainability refers to the ease with which the software can be modified or enhanced. It includes factors such as modularity, code readability, and documentation.

Within the maintainability quality factor, there are specific quality criteria. For example, one quality criterion could be code modularity, which assesses the extent to which the code is organized into separate and independent modules. Another criterion could be code readability, which evaluates the clarity and understandability of the code.

These quality criteria provide specific guidelines and specifications for evaluating the software's maintainability. They help in identifying areas for improvement and measuring the software's performance against the defined criteria.

Conclusion:
In the McCall quality model, the second level of quality attributes is known as product revision. This level focuses on the internal characteristics of the software that contribute to its overall quality. The quality factors at this level are further divided into quality criteria, which provide specific guidelines and specifications for evaluating the software's performance. By assessing the software against these criteria, organizations can identify areas for improvement and ensure that the software meets the desired quality standards.