Re-JIT is a new capability in CLR 4.5 that allows modification and recompilation of method-level IL code during runtime without requiring a process restart: so, the JIT runs again without shutting down executing applications. This is a great feature for instrumentation and profiling tools developers.
Here, we learn all about Re-JIT from one of the developers who wrote it: David Broman. Again, Re-JIT enables recompiling a method at runtime without restarting the process. Very cool.