Plagiarism is a serious issue and every writer needs to understand what it is and how to avoid it.
Plagiarism is taking other people's work and using it as if it were your own without acknowledging the source of this work. The work can be any product created by an individual or group of individuals. So, works of art, photographs, music, writing, reports, research, and many other creative endeavours are examples of products which must not be copied without permission.
This does not mean that you cannot refer to these products or use small samples of them for comment, criticism, or in the creation of new works. But what is acceptable use is something you need to understand. In writing you need to know how to quote See the glossary definition , paraphrase See the glossary definition , cite See the glossary definition and supply accurate references See the glossary definition to text from other authors which you have used in your own work.