GNU Radio is an open-source software toolkit that enables the development of software-defined radios (SDRs). It provides signal processing blocks to implement various radio protocols and allows users to create custom radio systems using a graphical interface or programming. With GNU Radio, users can process and analyze signals in real-time, making it useful for applications in telecommunications, research, and education. The toolkit supports a wide range of hardware, including USRP devices, and is widely used by hobbyists, engineers, and researchers to explore radio frequency communications.