D'Alembert's Ratio Test is a method used to determine the convergence or divergence of an infinite series. It involves examining the ratio of consecutive terms in the series. If the limit of the absolute value of the ratio of the terms approaches a value less than 1, the series converges. If it approaches a value greater than 1, the series diverges. If the limit equals 1, the test is inconclusive. This test is particularly useful for series where the terms involve factorials, exponentials, or powers. It provides a straightforward way to analyze the behavior of series without requiring complex calculations.