A practicum is connected to specific programs, such as teaching, counselling, some health jobs, etc. Other professions have similar periods (articling for law students, residence for doctors). Can be paid or unpaid. It should be a requirement of the program / mandatory.
Remember that in some provinces in Canada, unpaid internships are not allowed. They still exist. If you take one, you may be able to get paid for it afterwards through the government (but the employer will be mad at you and not give you references).