A geometric sequence is a type of sequence where each term is found by multiplying the previous term by a constant called the common ratio (r). It can be represented in the form a, ar, ar^2, ar^3, .... To identify a geometric sequence, we can check if the ratio between consecutive terms is constant. If the ratio is the same for every pair of consecutive terms, then we have a geometric sequence. For example, the sequence 2, 6, 18, 54, ... is a geometric sequence with a common ratio of 3.

In a geometric sequence, we can find any term using the nth term formula a_n = a * r^(n-1), where a_n represents the nth term, a is the first term, r is the common ratio, and n is the position of the term. For instance, in the sequence mentioned earlier, the value of the 5th term can be calculated as 2 * 3^(5-1) = 162.