A work specification is a document that describes the work that will be performed under a contract. It is sometimes called a Work Scope or Statement of Work.
In a Software Development Agreement, the work specification might describe the functionality of the application that the developer will deliver to the customer.
A work specification becomes part of an agreement when the agreement refers to it for information.
Often, the "separation of concerns" between an agreement and work specification is:
Here's an example of how an agreement and work specification would work together on the topic of payment.
The agreement would have a 'Payment Calculation' clause which refers to the work specification:
The fees payable to Provider in exchange for the Services will be calculated at the rate or rates set out in the Work Specification.
The work specification document would then set out payment rates, for example in a table like this:
Work type Rate (per day) UX Design \$400 Software design \$600 Web design \$300