Years between high school and undergrad, years off in undergrad, and years after undergrad all count as interruptions in your education. They want to make sure that if you are taking time off, you have a good reason/are doing something productive. A lot of people take a year or two to work in a lab before applying, and would use this type of essay to write about what they've been doing. If you did not go directly from high school to college, skipped a year in college, or are taking this year off, leave this essay blank at your own risk. If you decided to take a year off just to apply to medical school - not a great idea - find something worth mentioning to do (volunteering, research, etc..) asap.