A sequence is an ordered list of numbers or objects that follow a specific pattern or rule. Each number in the sequence is called a term, and the position of each term is important. For example, in the sequence 2, 4, 6, 8, each term increases by 2. Sequences can be finite, having a limited number of terms, or infinite, continuing indefinitely. They are commonly used in mathematics and can represent various concepts, such as arithmetic sequences, where the difference between terms is constant, or geometric sequences, where each term is multiplied by a fixed number.