As my colleague mentioned, there is no official definition in the act. For administration purposes, various definitions are used. The preamble to the Official Languages Act—I'm talking about the current version, so prior to the amending clauses that have been adopted so far—refers to English and French linguistic minority communities as integral parts of Canada's two official language communities, in other words, English and French.
It's implicit that the English linguistic minority community is in Quebec and that the French linguistic minority community is outside Quebec. The act doesn't say so in black and white, but that's basically how it works.