A monument is a statue or other sculpture meant to honor a great person, like the Lincoln Monument or Washington Monument.
You can find monuments in the downtown area of most cities. Many honor a specific person, while other are dedicated to soldiers who fought in a certain war, such as Vietnam or World War I. Cemeteries are also full of monuments, and monument can mean a type of burial vault. Whenever people create a monument, they're trying to make sure that a person or event is remembered.