I think I would use 'Absent', but in the US you see 'Incomplete'.

IN (Incomplete). The grade of IN (incomplete) may be given to a student who is passing a course but who may be unable to complete scheduled course work for a cause beyond reasonable control. The student must then complete all the requirements by the end of the ninth week of the next semester (not including Summer Term), and the instructor must turn in the final grade by the end of the tenth week. Unless an explicit written extension is filed with the Registrar's Office by the faculty deadline, the grade of IN is changed by the registrar to an F. Maximum IN extension is to the end of the same semester in which it was originally due. Students who have filed their intent to graduate have only six weeks from the date of degree conferral to resolve any incomplete grade(s) and have the final grade(s) recorded by the Registrar's Office.

https://www.gmu.edu/academics/catalog/0203/apolicies/examsgr...

Absence from examinations
Candidates for examinations are responsible for noting correctly the dates, times and location of their examinations.

No special arrangements can be made for candidates who fail to attend for examination at the proper time, if such failure is due to their mistake or inadvertence and not to illness or other serious and unavoidable cause.

https://www.dur.ac.uk/student.registry/assessment/exam_absen...