Noun
Oberth effect (uncountable)
(astronautics) The concept that the most efficient place for spacecraft to change velocity is at the periapsis (the lowest point of an orbit).
Some effects such as Oberth effect can only be significantly utilised by high thrust engines such as rockets, i.e. engines that can produce a high g-force (thrust per unit mass, equal to delta-v per unit time). Source: Internet
Oberth effect main One subtle feature of rockets relates to energy. Source: Internet