The term 'SERIES UNIT' can be broken down into two crossword solutions: EPISODE (7 letters) and STAGE (5 letters). An EPISODE is a part of a television or radio series, usually with a self-contained story. It is typically the smallest unit of a serial narrative, and is usually aired in a specific order. A STAGE is a division or portion of a process or journey, often divided into multiple parts. In terms of television and radio, a STAGE is a period of production in which a certain number of episodes are created.