Garrison ankle boots were for day-to-day wear in garrison or on a Canadian Forces base, out of the public eye (a “garrison” is a permanent military installation).
In the late twentieth century, when all black, all leather boots were a required part of the Army Combat Uniform, soldiers would have one set of field boots, which could get torn up during training, and one set of well-polished “spit-shined” boots for inspection, parades, or normal garrison duty. These boots could also be worn as part of the dress uniform.
Ankle boots (also known as parade boots) were a stiffer, more formal style of boot than combat boots and were slightly higher than the ankle. They were worn as part of working, walking out, and parade dress.