Plagiarism is getting the work of someone else and claim it as your own. It is a big no-no in university life and it could mean expulsion.
Sometimes people just get to tired to search and discover for themselves that they actually steal someone's idea to save their butts. How hard can it be? considering all the innovation that we have today in terms of researching. It's a big lie when we say that everything that can be discovered already exists.
On the contrary, there are a lot of things that we need to know. The world continuously moves and everything changes. Don't think you can't be caught when you plagiarize. Cheaters never win.