A transition state is a temporary configuration of atoms that occurs during a chemical reaction. It represents the highest energy point along the reaction pathway, where reactants are transformed into products. This state is crucial for understanding how reactions occur, as it helps chemists predict the speed and outcome of chemical processes. In the context of reaction mechanisms, the transition state is often depicted in energy diagrams, showing the energy changes throughout the reaction. The stability of the transition state influences the activation energy required for the reaction, which is a key factor in determining the rate of the reaction.