A common ratio is a term that appears frequently in the study of geometric sequences and series. It refers to the constant ratio between any two consecutive terms in a geometric sequence. In other words, the number multiplied (or divided) at each stage of a geometric sequence is called the "common ratio" because if you divide successive terms, youll always get this value. The common ratio formula helps in calculating the common ratio for a given geometric progression. The formula to find the common ratio of a geometric sequence is: r = n(^{th}) term / (n - 1)(^{th}) term. To calculate the common ratio in a geometric sequence, divide the n(^{th}) term by the (n - 1)(^{th}) term. The common ratio is a fundamental concept in the study of geometric sequences and series.