Halstead Volume is a software metric used to estimate the size and complexity of a program based on its source code. It is derived from the Halstead metrics, which analyze the number of unique operators and operands in the code. The volume provides insight into how much information is contained in the program, helping developers understand its maintainability and potential challenges. The formula for calculating Halstead Volume involves logarithmic functions of the total number of operators and operands. A higher volume indicates a more complex program, which may require more effort to understand and maintain. This metric is useful for software engineers and project managers in assessing code quality.