Final answer:
The difference between Kristen's estimate of 40 dogs and the actual number of 45 dogs at the dog park is known as an estimation error, which in this scenario amounts to 5 dogs.
Step-by-step explanation:
The term that best describes the difference between Kristen's estimate of the number of dogs at the dog park and the actual number is estimation error.
An estimation error occurs when there is a discrepancy between an estimated value and the true or actual value. In this case, Kristen estimated 40 dogs, but there were actually 45 dogs, which gives us an estimation error of 5 dogs.
It's important to note that making estimations is a common practice in many fields, including mathematics and statistics, and a certain degree of error is often expected.