Action symmetry
= Action symmetry
An infinitesimal transformation that preserves the <action> up to endpoint terms. For $\delta t=\varepsilon\phi$ and $\delta q_i=\varepsilon\psi_i$, invariance of $L\,dt$ yields the <Noether charge> $\sum_ip_i\psi_i-H\phi$, less any boundary-term generator.