The action of withdrawing from a course is taken after the add/drop courses deadline. Dropping a course refers to having the course removed from the student's schedule before the add/drop deadline.
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Refunds of matriculation and tuition fees are made only if official drop or withdrawal cards are turned in at the campus Admissions and Registration Office by the published deadlines (see Academic Calendar), or if you drop via the web (and the drop is confirmed) by the deadline.
It is better to drop the class. When applying to universities, if the program is not something that is needed for your program of choice, they will not look at dropped courses; it's as if you did not take it. But if you fail the course, it would be listed as failed and would not look good on your transcript.
If you must withdraw, you should always withdraw officially by going to your advisor or dropping the class on your student account. You should not withdraw from a class by not going to the class anymore.