If someone has done research of some kind of report on lab results, the data produced by a psychology experiment, or an essay delving into new interpretations of a historical period or famous book ― you can't simply copy it and pretend it is your own original material.

This prohibition applies to an author's thoughts as well as hard facts.  Just as you cannot copy someone's experiment data, you can't copy their theories, conclusions, arguments, or creative ideas.  Even J.K. Rowling faced plagiarism charges over her Harry Potter series, not for copying books wholesale but for allegedly borrowing concepts to help create her world.

Language matters.  Not just individual words, but sentence structure, metaphors, and style as well.  You can quote the original language directly, or put it completely into your own words, but you cannot just copy it.

Now, this doesn't mean you can't use someone else's facts, opinions, and language in your own work.  You can.  You just have to acknowledge it properly.  This involves telling the reader what your source is using conventional citation formatting, as well as indicating words that are not your own through quotation marks.  (This is where the historian Stephen Ambrose claims he messed up).

It shouldn't come as a surprise, but turning in a paper that you did not write yourself is academic dishonesty.  This includes papers found or bought online, papers someone else (a friend, a spouse, your pet) wrote for you, or a section of a book or article that you copied wholesale and passed off as your own.

You are expected to do your own work.

Plain and simple.  Don't cheat.

Let's say you find a really good article online and copy a paragraph or two (or five), figuring no one will notice or care.  Unfortunately, someone does care ― your professor, employer, etc.

Copying small amounts is no different than copying the whole thing.

Keep in mind that this is easy to do unintentionally: as you're pulling together material for your essay, it's easy to just copy and paste a few good sentences here and there without thinking about it.  But even accidental plagiarism is cheating.  Every word that you write in your paper is expected to be your own.  If it's not, it should be enclosed in quotation marks (" "), with a reference indicating your source.

Okay, so this is a little better than the previous example ― at least you've made some attempts to put the material into your own words, also known as paraphrasing.  But, if you haven't paraphrased correctly, and if you haven't given a reference to your source, you could still be in danger.

It can still count as plagiarism, even if you change some of the words.

Say you find a really good article that makes an excellent point about your topic.  You write a section of your paper (or just a sentence, or the whole thing) based on that article's argument, making sure that you put everything in your own words and don't use the exact wording of the original author.  Is that okay?  It's all your own work, so no need to mention that author in your paper, right?

Alas, no.

Copying someone's idea is just as bad as copying their words.

You see, the author of that article went to a lot of trouble to come up with those brilliant ideas.  You can't just pass them off as your own.

Now, if that article's argument is only used in a sentence or paragraph of your paper ― a support for your own original argument, nothing more ― then you're in good shape.  You've already done the work of paraphrasing, now just cite the author to let the reader know where those ideas came from and you're all set.

However, if your whole paper is based completely off someone else's idea, if you're just restating an argument already made elsewhere... then you're plagiarizing big time.

By now you know that copying someone else's paper is wrong, but what if you have a little help writing your own?  You wrote the paper, but then your friend helped you revise it, correcting some of the bad grammar and touching up the concluding argument.

When the help changes from reading over a paper to actually helping you write it, it's academic dishonesty.  The Academic Honesty Policy is pretty clear about this:

It is, for example, acceptable for a reader to suggest that a paragraph is unclear or needs more detail; it is unacceptable to offer specific rewording or details for inclusion. It is unacceptable to permit a typist or secretary to make changes or corrections in written material as part of the process of typing.

Of course, as the policy points out there are a few exceptions to this rule.

Your professor, the Writing Lab, and the Librarians here at Augsburg are good places to go to for help.

The key is understanding the difference between having your friend rewrite your paper for you and getting assistance from University staff who are here to help you and know when and where to stop. 

Check with your professor to make sure what help is allowed.

Sure, "Green" is in these days, but Reduce/Re-Use/Recycle isn't the best mantra for your term paper.  Let's say you wrote a paper for another course last semester that would be a perfect fit for your next assignment.  Can you reuse it?  The answer is maybe... but probably not.

Yes, you're not even allowed to copy your own work.

Professors expect your work to be fresh.  Reusing the paper would be like passing off a used car as brand new.  You may not mind a used car, but you wouldn't like it if you bought that car thinking that it had never been driven.  A few professors may be okay with a repurposed paper, but most won't.

Check with your professor ahead of time.

Otherwise, it's academic dishonesty, and last year's "A" paper could now get you an "F".

Keep in mind that this applies to portions of papers as well.  Copying a paragraph or two and pasting them into your report is not allowed.  Even if the papers are about similar topics, treat this as a good opportunity to rewrite and improve your ideas rather than simply repeat them.

The paper's due in the morning and you haven't done your research.  No harm in making a few fake citations to pad your sources, or creating a few numbers that seem to back up your claim, right?  Wrong.

Fabricating sources or evidence is academic dishonesty.

Your professor will probably know the truth instantly, and it's really easy to check to see if a source is valid or not.

It all comes back to the "Do your own work" concept, except here the key emphasis is on the "Do work" part.