In mathematics, HCF stands for "Highest Common Factor" or "Greatest Common Divisor". It is the largest positive integer that divides two or more integers without leaving a remainder. For example, the HCF of 8 and 12 is 4, which means that 4 is the largest number that can divide both 8 and 12 without leaving a remainder. HCF is also known as the "Greatest Common Measure" or "Greatest Common Divisor". It is useful in simplifying and comparing fractions. There are different methods to calculate the HCF, including prime factorization method and division method. HCF is introduced in Year 4 of the national curriculum, where pupils are taught to recognize and use factor pairs.