The only difference is when the request is submitted.
Courses are dropped during the drop/add period (usually the first week of classes). If you drop a class, it won’t appear on your official transcript or affect your GPA. However, dropping a class can have repercussions on financial aid.
If you leave a class later in the semester, you withdraw. You can withdraw with or without a “W” grade depending upon how far you are into the semester. Withdrawn classes appear on your official transcript but still aren’t calculated into your GPA.
If you simply stop attending class, you haven’t dropped or withdrawn. You will earn an “I” for the class, which stands for “Incomplete.” Incomplete classes appear on your official transcript and can affect your GPA.
In extenuating circumstances, a student can petition to withdraw from a class after the deadline.