When you sell investments like shares, which are deemed capital property to the Canada Revenue Agency (CRA), for more than you paid for it you have to declare this income as a capital gain. You are then taxed on a percentage of that gain, that percentage is referred to as the inclusion rate (the inclusion rate is currently 50%).
For more information on Capital Gains, please see the links below:
TurboTax - Capital Gains Tax in Canada
CRA - Capital Gains