Halstead Complexity is a software metric that measures the complexity of a program based on its operators and operands. It quantifies aspects like the number of unique operators and operands, as well as their total occurrences, to provide insights into the program's maintainability and understandability. The metric produces several values, including Halstead Length, Halstead Volume, and Halstead Difficulty. These values help developers assess the effort required to understand and modify the code, ultimately aiding in improving software quality and reducing errors during development.