Unitism is the principle that the value of land and nature is a shared inheritance that belongs to everyone, while the value people create through their own effort and enterprise belongs to them.
In practice, Unitism means communities fund themselves from the rental value of land — value the whole community creates — instead of taxing wages, sales, and buildings. You keep what you earn, and you pay for the exclusive use of a location. See the guides for how this works in detail, or read the book for the full argument.