For example, you need to place a copyright notification (for example, Copyright 2004. MyCompany publishing.) at the end of every page of a book. Instead of writing it every time, you could create an entity that represents this text: <!ENTITY copyright "Copyright 2004. MyCompany publishing."> where copyright is the name of the entity and "Copyright 2004. MyCompany publishing" is the text that the copyright entity represents.
To create an entity, follow these steps: