A grade is a categorical label assigned to a student's performance, mapped from raw marks via a published grade-band table. CBSE Class 10 uses a 9-band system (A1, A2, B1, B2, C1, C2, D, E1, E2). FBISE in Pakistan uses A+, A, B, C, D, E. American grading uses A, B, C, D, F with optional + and − modifiers (A−, B+).
The advantage of grading: it smooths out small mark differences. A student scoring 91% and one scoring 89% both land in the A1 band on CBSE and are treated as equivalent for admission purposes — which is arguably fairer than having a 2-mark difference decide a future.
The disadvantage: it compresses information. Two students with A1 grades could be 5+ marks apart, but a transcript shows them as equal. Universities that care about that resolution back-translate grades to percentage / grade points (this is what CGPA × 9.5 does for CBSE) before computing aggregates.
Grading scales vary widely by country and institution — always consult the specific board / university's published table before assuming a grade corresponds to a particular mark range.