to pour out: to empty something out of its container so it spills freely, whether liquid, contents, blood, or a gift given without stint
At its core this is the plain, everyday verb for pouring a liquid out of a vessel, and every use in the New Testament grows from that one picture: something held is tipped out and released completely. Wine spills from a torn wineskin, coins clatter across the floor, a man's insides burst open on the ground.
From that literal action the word stretches in three vivid directions. It becomes the standard way to speak of shedding blood, the violent spilling of a life, and in the Last Supper sayings it names the blood Jesus gives up for many. It pictures God emptying out his bowls of judgment on the earth in Revelation. And it describes God lavishing his Spirit and his love on people, poured out generously and without holding back.
What holds the range together is the image of a full container completely emptied. Whether the thing poured is water, blood, wrath, or the Spirit, the sense is the same: it comes out fully, freely, and often beyond measure. Only in one place does the word turn back on the person doing it, describing people who threw themselves recklessly into someone else's error.