The records include birth, marriage and death registrations and indexes. For a year at a time, those records are closed to researchers.
For example, in 2010 it was not possible to consult any birth registrations for the year 1914 (or marriage records for the year 1929, or death records for the year 1939.)
In 2011, those newly-microfilmed records were made available to the public, and the following records were closed: births in the year 1915, marriages in the year 1930, and deaths in the year 1940.
During the year of microfilming, the closed records are unavailable except in emergencies or other special circumstances.
To see a more complete explanation, visit the Ontario Vital Statistics page on the Archives of Ontario website.