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A **dependency** is the reliance of a piece of software on another piece of software. In the context of Minecraft Forge, it is a mod or library which another mod has a dependency on.
Dependencies are declared in three ways:
* The <code>dependencies</code> block in a Gradle buildscript defines compile-time and runtime dependencies, which is used by the build system and compiler when building or running the mod in the development environment.
* The act of using classes, fields, and methods from a library creates a dependency on the library in the compiled binaries. The library may be an explicitly declared dependency, or a dependency of an explicitly declared dependency (such as the Guava libraries that Minecraft depends on).
* [[Proper_Mod_Structuring#Dependency_Configurations|Dependency configurations]] are declared in the <tt>mods.toml</tt> metafile, which is then checked by Forge on runtime on whether they are satisfied.