Serial Wire Debug (SWD) is a two-wire protocol developed by ARM for debugging and programming microcontrollers. Unlike the traditional JTAG interface, SWD reduces pin count by using only a clock and data line, making it ideal for resource-constrained embedded systems. SWD allows developers to set breakpoints, step through code, and access memory or registers in real time. It is widely supported in ARM Cortex-M based devices and is commonly used for firmware development, troubleshooting, and device programming. SWD's simplicity and efficiency make it a preferred choice for modern embedded system debugging and in-system programming tasks.