What is the difference between a Debug and Release build?

What is the difference between a Debug and Release build? Is there a significant speed difference? Why or why not?

Release build is optimized for speed where as Debug is not because it's harder to pinpoint the location of bugs if it optimizes it first.

In debug mode, many of the compiler optimizations are turned off which allow the generated executable match up with the code. This allows breakpoints to be set accurately and allows a programmer to step through the code one line at a time. Debugging information is also generated help the debugger figure out where it is in the source code.

In release mode, most of the compiler's optimizations are turned on. Chunks of your code could be completely deleted, removed, or rewritten. The resulting executable will most likely not match up with your written code. However, normally release mode will run faster then debug mode due to the optimizations.