What is the meaning of Accuracy in results table? How is it calculated?
It is the number of unsuccessful tries made by you for solved problems.
So it measures how accurate you are when submitting the problems 
UPD.
Sorry. The previous notion corresponds to the penalty column in the rankings page like here:
The accuracy at the contest page is indeed what @kullalok indicated in the comment.
Are you sure it’s the unsuccessful tries made by “you”? There are several problems that I haven’t even attempted with an accuracy. From this, I assumed it was the percentage of successful submissions from the total number of submissions for all attempts made by anybody.