Large seal script is a style of writing Chinese characters that is very old and looks different from the characters we use today. It is called "large" because the characters are big and have a lot of space between the strokes.
Imagine writing a letter on a piece of paper, but instead of using small letters, you use big, fancy letters with lots of curves and lines. That's what large seal script looks like.
People in ancient China used large seal script to write important things like official documents and inscriptions on important objects. It was kind of like their fancy way of writing to make things look special and important.
Today, large seal script is mainly used for decorative purposes, like in calligraphy or on seals that people use to stamp their names on things. It is a beautiful and artistic way of writing that has been around for a very long time.