The Official Opposition, formally Her Majesty's Loyal Opposition (French: L'Opposition Loyale de Sa Majesté) is the position in Canadian government held by the second largest party, in the House of Commons. The role of the Official Opposition is to keep the government in check, similar to the oppositions in various other governments. The Official Opposition is called "Her Majesty's Loyal Opposition" to demonstrate that, although the group may be against the sitting government, it remains loyal to the Crown (the embodiment of the Canadian state) and thus to Canada. The current Official Opposition is the NDP.
Abilities
The Official Opposition party has advantages over other opposition parties in the House. They are assigned to speak first after the government, and receive more time in question period than other opposition parties. It also gets more office space, funding for research, and a larger staff than other parties. This generally means that the other opposing parties will want to form a coalition with the Official Opposition, to better leverage their powers, against the current sitting government.