What is the definition of static J - T distortion ?
The Jahn–Teller effect (J-T effect or JTE) is mechanism of spontaneous symmetry breaking in molecular and solid-state systems which has consequences in different fields, and is responsible for a variety of phenomena in stereochemistry, spectroscopy, crystal chemistry, molecular and solid-state physics, and materials science. The effect is named for Hermann Arthur Jahn and Edward Teller, who first reported studies about it in 1937.
There are static and dynamic JTE. In case of static JTE the system is trapped in one of the lowest-energy minima of the APES (usually determined by small perturbations created by the environment of the JT system) and does not have enough energy to cross the barrier towards another minimum during the typical time associated to the measurement. Quantum dynamical effects like tunnelling are negligible, and effectively the molecule or solid displays the low symmetry associated with a single minimum.