Intermediate Representation (IR) is the format that a compiler uses to represent code internally. Typically, this is neither the compiled language, nor the native code, but something more generic in between. An IR format should lend itself well to optimization and transforms. In JRockit, the intermediate representation has several tiers, the top tiers looking more like Java code, and the bottom tiers looking more like native code. This is a fairly standard approach.

See also HIR, MIR, LIR, Register allocation, and Native code.