Subsequence

A subsequence of a Sequence $S=\{x_i\}_{i=1}^n$ is a derived sequence $\{y_i\}_{i=1}^N = \{x_{i+j}\}$ for some $j\geq 0$ and $N\leq n-j$. More generally, the word subsequence is sometimes used to mean a sequence derived from a sequence $S$ by discarding some of its terms.

See also Lower-Trimmed Subsequence, Upper-Trimmed Subsequence