Nick Morris describes the four major types of plagiarism as follows below. The following excerpt is taken from his webpage, with his kind permission.

• ‘Text’ - copying text from a book, paper, document etc.
• ‘Diagrams & Program’ - copying a diagram or a program
• ‘Idea’ - passing off another person’s idea as your own
• ‘Auto’ - copying from yourself!

Text Plagiarism: This is the most easy to understand, and the most common form of plagiarism. Basically it is the copying of text from some source (a paper, text book, fellow student, internet) into your own work, and then passing it off as your own. It should be noted that adding a reference (i.e. stating from where you copied the text) is no 'protection' and doesn't mean you can copy (unless it has been explicitly allowed). If you find yourself reaching for the copy and paste keys on the computer then there is a good chance it will be plagiarism.

Diagram & Code Plagiarism: This is where you copy a diagram, figure or a chunk of code from somewhere else and pass it off as your own (this can also be viewed as 'idea' plagiarism as some one has thought long and hard about creating the figure or code). Note that, straightforward modifications to the original figure or code is still considered plagiarism.

Idea Plagiarism: This is the worst form of plagiarism as you would be attempting to pass off the hard work, and intellectual property, of a fellow person as your own. You can write about the ideas and thoughts of others, but YOU MUST STATE FROM WHERE YOU GOT THE IDEA. Basically, this is one of the reasons why we reference sources of information, you are stating who had the original idea, and how they came by it. Effectively by referencing you are acknowledging the hard work of the others.

Auto-Plagiarism: This form of plagiarism is the one most people have difficulty understanding. After all, how can you plagiarise yourself? You 'own' the work and the intellectual property! Well, basically auto-plagiarism would occur if you handed in the same piece of work for two different assignments and got two lots of marks for it. Or put another way, it is like making one burger in McDonald's and selling it twice.