Level pace compensates for how hills slow you down and speed you up in running, to provide a neutral interpretation of your workout.
You may be training to improve various parts of your run, such doing speedwork or working on your form, but, you likely don't run on identical courses everyday. This can make it difficult to determine if you're improving or not, because it's hard to compare one run against another.
Level pace (which is also known as Grade Adjusted Pace) provides a way to equally compare your performance from workout to workout, regardless of how hilly the various courses may have been.
Find it in SportTracks
You can find level pace in on your Workout Detail pages for running workouts by clicking the Total Block for pace at the top: