Compiled code is code that is translated into a low-level language, such as C, C++, or Fortran, and executed directly by the machine, instead of being interpreted by R. This approach can run faster and more efficiently than interpreted code, as it avoids the overhead and limitations of R, such as memory management and type checking. R offers several ways to use compiled code, including the Rcpp package that provides functions and classes to integrate C++ code with R; the inline package which allows users to write and compile C, C++, or Fortran code within R; and the R CMD SHLIB command which compiles C, C++, or Fortran code into a shared library that can be loaded by R using the dyn.load and .C or .Call functions. By utilizing these methods, you can create high-performance and user-friendly functions that can be called from R.