Plagiarism is a blanket term for copying somebody's content directly or the idea for their content.
In the academic world, you get accused of plagiarism not just in cases where you copy and paste somebody else's work without giving them credit, but you also get penalized for lifting their ideas.
This is what got Martin Luther King, Jr. in trouble. He got into the habit of using other people's ideas in his dissertation without proper attribution.
On the other hand, the copyright is more specific to the form of the content.
For example, if I write an article using a particular sentence structure and stringing certain words together, I can copyright that.
If you copy and paste it, I can sue you, or I can get your server to pull your content from the internet.
But if you were to take my ideas or the information that I have presented in my article and [/b]put it in your own words[/b], that isn't covered by copyright.
Generally speaking, that is not covered by copyright unless you can argue that this is derivative content. In other words, I could not have made this piece of content without your stuff.
But that's really hard to prove because, on the internet, it seems that content you find in one place is actually just a mishmash of information found elsewhere but presented in a person's unique words.
For SEO purposes, duplicate content is the main issue.
So if you're just going to copy and paste somebody else's work, chances are, Google will show your content result below the original. Google's algorithm is structured to reward the "original instance" of the content with a higher ranking.
This doesn't always work.
In fact, the guys from <b>Income School</b> are complaining that some people are copying new posts to their website before it gets indexed.
So what happens is that these copies get indexed first.
But, of course, since the Income School guys own the copyright to that material, they can always sue or put pressure on the server hosting those pages to get them taken down.
Still, it's a massive headache.