Series refers to a group of related items arranged in a logical or chronological order — such as books, TV episodes, products, or biological classifications. The character 系 (xì) means 'system', 'category', or 'lineage', suggesting connectedness or classification; 列 (liè) means 'row', 'list', or 'sequence', emphasizing orderly arrangement. Together, 系列 conveys the idea of a structured, coherent set where each member belongs to the same family, type, or progression.

This noun is widely used in everyday and formal contexts: product lines (e.g., iPhone series), academic disciplines (e.g., lecture series), media (e.g., documentary series), and scientific taxonomy (e.g., animal series in biology textbooks). It’s neutral in register and often appears after classifiers like 一 (yī) or adjectives like 新 (xīn, 'new') or 整套 (zhěng tào, 'complete set'). Unlike English 'series', 系列 is always singular in form — no plural marking — and rarely used without a modifier or context specifying its scope.