Term: trajectory https://doi.org/10.1351/goldbook.T06431 Definition: A path taken by a reaction system over potential-energy (reaction) surface or a diagram or mathematical description that represents that path. A trajectory can also be called a reaction path. Related Terms: 1) potential-energy (reaction) surface (http://doi.org/10.1351/goldbook.P04780). 2) reaction path (http://doi.org/10.1351/goldbook.R05174). Source: PAC, 1996, 68, 149. 'A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)' on page 189 (https://doi.org/10.1351/pac199668010149) Citation: 'trajectory' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.T06431 License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms. Disclaimer: The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.