What is Gibbs energy, enthalpy and entropy of activation?

The Gibbs energy of activation $\Delta^{\ddagger}G^\circ$, enthalpy of activation $\Delta^{\ddagger}H^\circ$ and entropy of activation $\Delta^{\ddagger}S^\circ$ of an elementary step are the standard Gibbs energy, enthalpy and entropy of formation of the activated complex (without its reaction-coordinate motion) from the reactants, defined by the Eyring equation.