Terms are the numbers of a sequence. For example, the numbers $4$ and $7.5$ are terms in the set $\mathbb{R}$ (the real numbers). In the sequence $a_1, \ a_2, \ldots,\ a_i, \ldots, \, a_n$ the term $a_n$ can represent an arbitrary term in the sequence, where $n$ gives its position. Alternatively, if the sequence is finite, $a_n$ can represent the last term of the sequence, and the index $n$ gives the number of terms in the sequence.