Numba is a just-in-time compiler for Python that can optimize numerical code to achieve speeds comparable to C/C++ without requiring the user to write C/C++ code. It works by compiling Python functions to optimized machine code using type information. Numba supports NumPy arrays and common mathematical functions. It can automatically optimize loops and compile functions for CPU or GPU execution. Numba allows users to write high-performance numerical code in Python without sacrificing readability or development speed.