What is plaggierism?

Answer 1

There is no such English word as "plaggierism".

However, "plagiarism" happens when someone takes someone else's work or ideas and passes them off as their own.

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Note. it is OK to use someone else's work, this is a good thing, but when you do you should always reference (acknowledge) the source you took it from. Not to do so is cheating/stealing.