In the City-wide Zoning By-law 569-2013 a secondary suite is defined as:

self-contained living accommodation for an additional person or persons living together as a separate single housekeeping unit, in which both food preparation and sanitary facilities are provided for the exclusive use of the occupants of the suite, located in and subordinate to a dwelling unit.

In Toronto’s Residential zones, one Secondary Suite is generally permitted within a dwelling unit in a Detached House, Semi-Detached House or Townhouse, subject to performance standards in Section 150.10 of Zoning By-law 569-2013.