A commemorative plaque is like a special sign that people put up to remember something important. It's like a small flat piece of metal, wood, or stone with words and pictures on it to celebrate and remember something special that happened in the past.
For example, if a group of people wanted to remember a famous person who lived in a particular house, they could put up a plaque outside that house so that everyone who walked by would know the house's significance. It could say something like, "The Famous Writer Jane Austen lived here from 1809-1817."
People can also put up commemorative plaques to remember important events like the opening of a new building or the anniversary of a historical event. These signs usually have words and pictures that describe the event and why it's important to remember.
In short, a commemorative plaque is a special sign that celebrates and remembers an important person, place or event.