Simply put, remediation is a form of assessment offered to students who fail to meet the requirements of a particular course(s). These requirements are outlined in the course syllabus and may involve passing specific assignments, exams, OSCEs, etc.
For example, if a course requires a student to pass both the midterm and the final, and a student fails the final, that student may be offered a chance to remediate and write a supplementary final exam. If the failed component is an OSCE, the student will be required to complete a supplementary OSCE. These are the most common supplemental assessments that take place but the assessment type itself can vary depending on what the failed component is.