Perennial:(of plants) continuing to live from year to year
Would you kindly explain this part: from year to year?
That the plant lives from year to year means that it does not die after one year — or, more accurately, one growing season.
In fact, the explanation for perennial from Wikipedia makes this more clear:
A perennial plant or simply perennial (from Latin per, meaning "through", and annus, meaning "year") is a plant that lives for more than two years
As you can see, the dictionary definition isn't even entirely correct, as the plant indeed has to live for more than two years to be considered perennial.