Montreal Olympic Stadium is a multi-purpose stadium in Montreal, Canada, located at Olympic Park in the Hochelaga-Maisonneuve district of the city. Built in the mid-1970s as the main venue for the 1976 Summer Olympics, it is nicknamed "The Big O", a reference to both its name and to the doughnut-shape of the permanent component of the stadium's roof. 

The tower standing next to the stadium, The Montreal Tower, is the tallest inclined tower in the world with an angle elevation of 45 degrees. It is also called "The Big Owe" to reference the astronomical cost of the stadium and the 1976 Olympics as a whole.

The stadium is the largest by seating capacity in Canada. After the Olympics, artificial turf was installed and it became the home of Montreal's professional baseball and football teams. The Montreal Alouettes of the CFL returned to their previous home of Molson Stadium in 1998 for regular season games, but continued to use Olympic Stadium for playoff and Grey Cup games until 2014 when they returned to Molson Stadium for all of their games. 

The stadium currently serves as a multipurpose facility for special events (e.g. concerts, trade shows) with a permanent seating capacity of 56,040. 

According to en.wikipedia