Impulse energy buffer (also called verteron buffers) were a technology used to minimise the effects of starship impulse engines.
Following the discovery of the Bajoran wormhole and the existence of the Prophets, any starship crew that required access to the wormhole had to drydock their vessel at Deep Space 9 to have impulse energy buffers mounted around their impulse engines. Some races, like the Cardassians, disliked having to do so. (DS9 novel: Bloodletter)
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The concept originated in the DS9 series bible and early drafts of "Emissary" (The Making of Star Trek: Deep Space Nine), but did not make it to screen.