Source code is a set of instructions written in a programming language that tells a computer how to perform specific tasks. It serves as the blueprint for software applications, allowing developers to create programs that can run on various devices. Common programming languages include Python, Java, and C++. When developers write source code, they often use an integrated development environment (IDE) to help organize and edit their work. Once the code is complete, it is compiled or interpreted into machine code, which the computer can understand and execute. This process is essential for creating functional software.