Plagiarise - "Take and use as one’s own (the thoughts, writings, inventions etc., of another person); copy (literary work, ideas etc.) improperly or without acknowledgement; pass off the thoughts, work, etc., of (another person) as one's own."
From: The New Shorter Oxford English Dictionary.
The only source you can use in an essay without crediting it, is information that is considered common knowledge and as a result not attributable to one source.
Common knowledge is information generally known to a knowledgeable person, such as commonly known facts and dates.
Examples of common knowledge are:
URKUND is an automatic text-recognition system made for detecting, preventing and handling plagiarism.
URKUND shows lecturers’ how much of a student's work matches content from their databases; so they can understand how much of the work is original.
Plagiarism is closely related to academic integrity and is a serious academic offence.
ATU Galway-Mayo Policy on Plagiarism:
Plagiarism cover sheets:
Login required (registered students & staff).
The authors of Cite them right share their top tips to help you correctly acknowledge sources.
Whether quoting, paraphrasing or summarising, using someone’s work without crediting the source can lead to claims of plagiarism.