Plagiarism is the use of another's work (including your own previous work) without clearly indicating of the source of the information. Another's work doesn't just mean their words it also covers their ideas, images, statistics, data, etc.
Plagiarism may be deliberate or accidental - you should avoid both types.
As well as the work of other authors you must also cite and reference your own previous work, not doing so is called self-plagiarism.
Self-plagiarism occurs when an author reuses substantial parts of his or her own work without providing the appropriate references.
