What does "per Centum per Annum" mean?

It refers to the interest or to an income or annuity. Per centum you ought to recognize as "per cent." It means for each 100. And per annum means for each year. So judging just by what you have so far the person may be receiving $8 each year for every $100 he has in the bank. That would be the simplest explanation, though it may be that he is receiving a percentage of $8 each year.