The Estus Flask is a healing item featured in the video game series Dark Souls. It allows players to restore health during their journey through challenging environments and battles. The flask is filled with a magical substance called Estus, which replenishes the player's health when consumed. In the game, players can find and upgrade the Estus Flask at specific locations, enhancing its healing capabilities. The flask is a crucial resource, as it helps players survive against formidable enemies and bosses, making it an essential part of the gameplay experience in the Dark Souls universe.