The word Ecthesis, from the Greek εκθεσις meaning a "statement of faith", was used famously as the title of a thesis by emperor Heraclius in 638 to state a heretical formula forbidding the mention of "energies".
It forbade the mention of "energies," either one or two, in the person of Jesus Christ. It also asserted that the two natures of Christ were united in a single will (i.e., Monothelitism). It had been drafted earlier in 638 by Patriarch Sergius I of Constantinople after consultation with Pope Honorius of Rome. It was accepted by synods held in the Imperial capital, but quickly repudiated by Heraclius as well as Honorius' two successors (Popes Severinus and John IV).
It was later superseded by Emperor Constans II's Typos.
The text of the Ecthesis is preserved in the Acta of the Lateran Council of 649.
The Oxford Dictionary of the Christian Church (3rd ed.), p. 528