Resonance is a fundamental concept that is necessary for students' successful learning in organic chemistry. However, there is a need to know more about both (1) what students find important when describing resonance and (2) students' conceptual understanding. This research seeks to address this discrepancy by examining second-semester organic chemistry students' responses to a writing-to-learn (WTL) assignment focused on resonance. This work is guided by the cognitive process theory of writing and studies within undergraduate STEM and chemistry courses that indicate the usefulness of WTL assignments for examining how students convey their understanding of fundamental concepts. We analyzed students' responses to a WTL assignment designed to elicit students' explanations of resonance and its influence on reactivity to a general, nonscientific audience. The goal of our analysis was to identify the features students found important when explaining resonance and to gain insight regarding their conceptual understanding. The analysis was guided by an analytical framework outlining the learning objectives for resonance at the introductory organic chemistry level. We identified various elements in students' writing, including (1) the analogies or examples students used to explain resonance, (2) the basic definitions of the concept students included, and (3) the various ways students described the influence of resonance on reactivity. Our findings indicate that students generally described resonance with an operational rather than conceptual definition, focusing on the process of drawing resonance structures rather than providing conceptual explanations. Furthermore, we identified that students tended to associate resonance with stability, with many students often extending this association to make overgeneralized statements about the influence of resonance on reactivity.