A middle (junior high) school teaches grades in between a primary (elementary) and secondary (senior high) school. Only some provinces have the concept, while others divide the "middle" years between primary/elementary and secondary/senior. See a table of grade structure by province for how different provinces divide their grades. Sometimes what's considered in one place to be a middle school, may be classed as elementary or high school elsewhere (even within the same province), so it may be necessary to look at one of the other categories if a school is not present here.
Related categories for Canada:
Subcategories
This category has the following 9 subcategories, out of 9 total.