Cheating is the actual or attempted practice of fraudulent or deceptive acts for the purpose of improving one's grade or obtaining course credit; such acts also include assisting another student to do so. Typically, such acts occur in relation to examinations, projects, labs, or homework.  However, it is the intent of this definition that the term “cheating” not be limited to above listed situations only, but that it include any and all actions by a student that are intended to gain an unearned academic advantage by fraudulent or deceptive means.

Plagiarism is a specific form of cheating which consists of the misuse of the published and/or unpublished works of others by misrepresenting the material so used as one's own work. 

Penalties for cheating and plagiarism range from a 0 or F on a particular assignment, through an F for the course, to expulsion from the college. Plagiarism can include submitting a paper written by someone else as your own;

-written by means of inappropriate collaboration;
-written by you for another course, submitted without the permission of both instructors;
-purchased, downloaded, or cut and pasted from the Internet;
-or that fails to properly acknowledge its sources through standard citations.

http://owl.english.purdue.edu/handouts/research/r_plagiar.html
(tips on how to avoid plagiarism from Purdue University)