Plagiarism refers to copying the words and ideas of someone else and claiming them to be your own.
It is more common in content writing where some freshers do not understand the repercussions of plagiarism and copy content from other web pages. It is a type of intellectual theft and must be avoided at all costs.
Putting plagiarized content on your website can attract legal proceedings either under copyright law or if the original owner of the content files a report against you.
Google will also not regard plagiarized content as worthy and your webpage will not rank among the top search results.