Plagiarism is defined as:
the unacknowledged use of someone else’s work. This includes material or ideas from any (published or unpublished) sources, whether print, electronic (even if freely available on the internet) or audiovisual. Using the words or ideas of others without citing and referencing them would be construed as plagiarism, and is a very serious academic offence. At the end of the day, it is regarded as the stealing of intellectual property (Pears and Shields, 2019, p. 4).
When you plagiarise, you pass off someone else’s work, whether intentionally or unintentionally, as your own for your own benefit. You quote, paraphrase, summarise or copy material without acknowledging the original sources. When you plagiarise, you are not following correct referencing guidelines. You are guilty of academic dishonesty.
Source: NEIU Libraries (2020) What is academic honesty?
Image source: http://libguides.butler.edu/plagiarism
The Complete Guide to Referencing and Avoiding Plagiarism by 
The Library, Technological University of the Shannon: Midwest