Harvard University Police Department is a group of people who make sure that everyone on Harvard University's campus is safe and following the rules. This means that they help to make sure that people are not hurting each other, breaking things, or stealing things.
They wear a special uniform and have special training so they know how to take care of everyone on the campus. They also work closely with other police departments in the area if they need help with something.
If someone on the campus is in trouble or needs help, they can contact the Harvard University Police Department and they will send someone to help them. They might also help with things like lost and found items or making sure people are parked in the right spots.
Overall, the Harvard University Police Department is a group of people whose job is to keep everyone safe and make sure that things are running smoothly on campus.