This article describes the differences between enrollment status in Canvas, and how to manipulate the enrollments in a Canvas course.
A Canvas course enrollment, or "seat", can be in one status out of several. When enrolling in a course, a student will enter the course with the enrollment status of "Active". While in this status the student has normal "student access" to the course. If the student un-enrolls or is dropped from the course their enrollment status will change to "Concluded" (shows as "Completed"). While in this state the student will not have access to the course and the course will not show on the student's course listing. The student will also not be listed in the main people listing, nor in the grade center.
You may also see students in your Canvas course people listing tagged as "Inactive". This is the "old" status and is being transitioned to "Concluded". This will be done automatically by Canvas Operations, and no action is required on your part.
There is no "drop" or "un-enroll" within the Canvas environment. To remove a student's enrollment from your course you need to "Conclude" the enrollment:
NOTE: if the student does not show up in the people listing or in previous enrollments, they are no longer a member of your course.