What is a benchmark model?
Benchmarking is the process of comparing your result to existing methods. You may compare to published results using another paper, for example. If there is no other obvious methodology against which you can benchmark, you might compare to the best naive solution (guessing the mean, guessing the majority class, etc) or a very simple model (a simple regression, K Nearest Neighbors).  If the field is well studied, you should probably benchmark against the current published state of the art (and possibly against human performance when relevant).