The sale of certain property or shares can result in a capital gain. Line 12700 lists the taxable portion of your capital gains – losses and rate (usually 50%) applied.
Capital gains information can be from T slips such as T3, T4PS, T5, T5008, and T5013 or entered separately.
If, after all of your capital gains and losses have been entered, you have a net capital loss, line 12700 will be zero. The loss will be carried forward for future years or can be carried back against previous gains.