A coemeterium is a fancy word for a place where people are buried after they die. It's like a really big and special place with lots of different sections for different people. They can be above ground with lots of little houses, or underground with lots of little rooms.
When someone dies, their family and friends can choose to bury them in a coemeterium so that they can visit them and remember them. People might also choose a coemeterium if they don't have a place to bury their loved one, or if their religion or culture requires a special way of burial.
Coemeteriums can be really peaceful and pretty, with pretty flowers and trees. Sometimes people even make special decorations or put up little statues or pictures to remember the people who were buried there.
Overall, a coemeterium is like a very special and important place where people go to remember their loved ones who have passed away.