Halstead metrics are a set of software metrics used to measure the complexity of a program based on its source code. Developed by Maurice Halstead in the 1970s, these metrics focus on the number of unique operators and operands in the code, allowing developers to assess the effort required to understand and maintain the software. The key components of Halstead metrics include measures such as program length, calculated difficulty, and estimated effort. By analyzing these metrics, developers can gain insights into code quality, potential bugs, and the overall maintainability of the software, helping to improve development practices.