Canon is the yearly fee the local municipality calculates for ground that is issued by the municipality bases on ground lease (in use). Just like the interest on a mortgage this amount is tax-deductible.
There is also such a thing as private ground lease. In this case not the city of Amsterdam is owner of the ground, however a private person is. A house with private ground lease has limited financing options. Furthermore, the private ground lease situation has negative impact on marketability of the house.