Final answer:
Benchmarking is the term that best describes the evaluation of the nursing unit's central line site infection rate.
Step-by-step explanation:
The term that best describes the evaluation of the nursing unit's central line site infection rate is benchmarking. Benchmarking involves comparing an organization's performance to a standard or benchmark, which in this case is the agency's expected standard of a 5% infection rate. The nursing unit's infection rate of 3% is lower than the expected standard, indicating that the implementation of the new protocol has been successful in reducing infections.