The Non-Resident Speculation Tax also known as NRST is an additional 20% tax on the purchase of a residential property located in Ontario.
This an additional tax on top of the general land transfer tax in Ontario. It's only applicable to individuals who are not citizen or not a permanent resident of Canada or purchasing as a foreign corporation (foreign entity).
Also, other types of land such as land containing multi‑residential rental apartment buildings with more than six units, agricultural land, commercial land or industrial land don't apply to the NRST.
Exemptions and Rebates
There are some exemptions and refunds available. For example. if you are a foreign buyer but your spouse has been a citizen, permanent residence or is nominated under the Ontario Immigrant Nominee Program consequently for more than 3 years.
You can also get a rebate. For instance, if you become a citizen within 4 years of the purchase or if you are a full time international student and enrolled full-time at least two years from the date of purchase. You also may get a rebate if you worked full-time under a valid work permit in Ontario for at least one year since the date of purchase.
For more complete information please refer to this government bulletin: