In this context, the word “prohibition” refers to laws that banned the use of alcohol. In the United States, prohibition was in effect for over a decade. Canada did not have such an extended period of prohibition at the national level. Instead, there was only national prohibition for just two years. There were provinces in which prohibition was in effect for longer periods, but only Prince Edward Island continued to have prohibition on the provincial level after 1930.
Prohibition was a popular idea among Canadian social reformers for quite some time. They believed that the use of alcohol was something that was bad for society and for those who actually drank. They felt that banning alcohol would do away with many of the social problems that faced their nation. These reformers were able to persuade many local governments to ban alcohol at the local level. In 1901, prohibition was implemented on a provincial level for the first time. Between then and WWI, other provinces joined in. During the later part of WWI, prohibition was implemented on the national level, in part as a war readiness measure.
So, prohibition refers to laws that were passed that banned the use of alcohol. Prohibition existed for a short time at the national level and for a longer time in various provinces.