Scoring

A player's performance on a map is given in terms of score after a successful completion of the map. Most of the time, combo plays the major part in the scoring system since it serves as a multiplier of the score. The only score limiter known now is osu!mania, which is capped at 1,000,000 score at 1.00x score boost. The rest are not capped, which can result in ridiculous level of score due to the combo multiplier effect.

osu!standard
Normal Grades:

SS = 100% Accuracy.

S = Over 90% 300s, less than 1% 50s and no misses.

A = Over 80% 300s and no misses OR over 90% 300s.

B = Over 70% 300s and no misses OR over 80% 300s.

C = Over 60% 300s.

D = None of the above.

Taiko
Normal grades

SS = 100% Accuracy.

S = Over 95% Accuracy (90+% GREATs, or less than 1 GOOD for every 10 notes).

A = Over 90% Accuracy (80+% GREATs, or less than 1 GOOD for every 5 notes).

B = Over 80% Accuracy (70+% GREATs, or less than 1 GOOD for every 3.33 notes).

Catch the Beat
Normal grades

SS = 100.00% Accuracy S = 98.01% to 99.99% Accuracy (You can have 'S' rank even if you make several misses).

A = 94.01% to 98.00% Accuracy

B = 90.01% to 94.00% Accuracy

C = 85.01% to 90.00% Accuracy

D = Any other accuracy under 85.00%.

osu!mania
Normal grades

SS = 100% Accuracy (only MAX and/or 300).

S = Over 95% Accuracy (You can achieve an 'S' rank even if you make several misses).

A = Over 90% Accuracy.

B = Over 80% Accuracy.

C = Over 70% Accuracy.

D = Anything else.

Other Grades
Special Grades: Regarding the "Ranks" in profile page
 * Silver SS (SSH) = Normal SS with hidden and/or flashlight mod.
 * Silver S (SH) = Normal S with hidden and/or flashlight mod.
 * Grades you obtained will be set at your profile page under General.
 * Ranks provided you are online when receiving the grade.
 * Offline play even when your account is logged in is not counted.
 * Grades given for your profile depends on beatmap difficulties, not as whole.
 * If the beatmap has 3 difficulties, and you SS all three of them, you will receive 3 SS and not just one SS in your profile.