If the student is currently enrolled in an Active class, their Enroll Type = Enrolled and Class(es) appear in the Current Enrollment section of the student's Classes tab.
The student did not complete the class. The student was dropped before the class was completed using the Drop link. This is considered a 'true drop' and will appear on the Drop History Report. If a student is dropped from a class, the class appears in the Past Enrollment section of the student Classes tab. Note: It's important to archive classes (rather than drop students from class after it ends) so that reports will only display 'true' drops. See Archive Classes.
A student is considered transferred when they have been moved from one class to another. This creates a Past Enrollment record, but this is not considered a drop. It is treated as a Transfer and does not negatively reflect on the school / class / teacher and is excluded form the drop reports.
The ability to enroll in a class as a trial is a per class option. When a student enrolls into a class on a trial basis, their Enroll Type = Trial. See Trial Enrollment.
If a trial student enrolls in class, it is good practice to change the student Enroll Type to Trial-Enrolled. See Trial Enrollment.
In the Past Enrollment section (Student Classes tab), the Comp? column indicates whether the student completed the class (Yes) or did not complete the class (No.)