A geometric progression is a sequence of numbers where each term after the first is found by multiplying the previous term by a fixed, non-zero number called the common ratio. For example, in the sequence 2, 6, 18, 54, each term is multiplied by 3 to get the next term. Geometric progressions can be used in various fields, including finance, physics, and computer science. They help model exponential growth or decay, such as in population growth or radioactive decay. The formula for the nth term of a geometric progression is given by a_n = a_1 * r^(n-1), where a_1 is the first term and r is the common ratio.