The conditions that govern how a dataset or service may be used, accessed, and redistributed.
Terms of use (also called terms and conditions or a data licence) set out what you are and are not allowed to do with data. They may permit or restrict commercial use, redistribution, modification, attribution requirements, and the creation of derivative works.
For open data, terms of use are typically expressed through a standard open licence such as the Open Government Licence – Canada or a Creative Commons licence. For restricted data, terms of use may be set out in a data sharing agreement.
Example: A mapping service's terms of use permit personal and non-commercial use of its data but prohibit using the data to build competing commercial products. A developer who builds a paid navigation app using that data without a commercial licence is violating the terms of use.
Always read the terms of use before downloading or using a dataset. "Free to access" does not always mean "free to use for any purpose."