In Canada, the prime rate is a guideline interest rate used by banks on loans for their "prime" clients. The prime rate rises and falls with the Canadian economy. It is significantly by the overnight rate, which is set by the Bank of Canada.
The prime rate is especially important to variable rate mortgages, which rise and lower with the market. Typically mortgage customers get a discount off of the Prime Rate (Example: Prime being 2.70%, their rate is Prime -.40%, or 2.30%).