Reducing agent may be defined in various ways, depending upon the context in which the phrase is used. In broad terms it is often taken to mean a chemical which can act as an electron donor. Thus, in the reaction:
the zinc is being reduced (gaining electrons) by reaction with the iron cations; the Fe2+ in this instance is acting as a reducing agent.
Generalic, Eni. "Reducing agent." Croatian-English Chemistry Dictionary & Glossary. 29 June 2022. KTF-Split. {Date of access}. <https://glossary.periodni.com>.
Glossary
Periodic Table