The Ratio Test is a method used in calculus to determine the convergence or divergence of an infinite series. It involves examining the limit of the absolute value of the ratio of consecutive terms in the series. If this limit is less than 1, the series converges; if it is greater than 1, the series diverges. If the limit equals 1, the test is inconclusive, and other methods must be used. To apply the Ratio Test, you calculate the limit as n approaches infinity of \left| \fraca_{n+1}a_n \right| , where a_n represents the terms of the series. This test is particularly useful for series involving factorials or exponential functions, as it simplifies the analysis of their behavior.