debian mentors/ glossary/ Build Dependencies
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Build Dependencies

Build dependencies are specified in a source package and give information about what packages must be present on the system.

There are two types, Depends and Conflicts. They work in a similar way to normal Depends and Conflicts, in that Depends must be installed, and Conflicts cannot be installed.

There is also a distinction between -Indep dependencies and normal ones.

There is more information at http://www.debian.org/doc/debian-policy/ch-relationships.html#s-sourcebinarydeps