Income from a resource above what is needed to bring it into use, typically arising from scarcity, location or legal privilege rather than effort or investment.
In more detail
In classical economics, land rent is the main example: the value of a central plot reflects public infrastructure and community growth, not the owner's work. Henry George argued that taxing land rent would capture this unearned increment without discouraging production. The concept extends to natural-resource rents, monopoly profits and licences. Taxing pure rents is efficient in theory because it does not change behaviour, but in practice rents are hard to separate from returns to investment.