Plain-English definition. A Canada Visitor Visa is a Temporary Resident Visa (TRV) that lets you enter Canada for a limited period for tourism, family visits, or certain business visitor activities. It is not a work permit and it is not a study permit. Some travellers don’t need a TRV and instead travel on an eTA (electronic Travel Authorization) if they’re from visa-exempt countries; which one you need depends on your nationality and how you enter Canada (air vs. land/sea). Check your document type before you book flights; U.S. citizens don’t need a visa or eTA, and U.S. lawful permanent residents need an eTA to fly.
Single vs. multiple entry. Most TRVs issued today are multiple-entry, which simply means you can be admitted repeatedly while the visa is valid. It does not lock in how long you can stay each time; that’s decided at the border.