4-bit machine language is a type of low-level programming language where both instructions and data are represented using 4 bits (half a byte). This architecture was common in early microprocessors and simple embedded systems, where memory and processing power were extremely limited. Each instruction or data value can represent 16 possible combinations (2^4), restricting the complexity and range of operations. While largely obsolete today, 4-bit machine languages are still studied for educational purposes and occasionally used in ultra-simple digital devices or retrocomputing projects.