People use this word for huge, planned jobs that try to cool the planet on purpose, because the Earth is getting too warm. There are two main kinds, and they do not feel the same. One kind tries to pull carbon dioxide out of the air — the gas from cars, factories, and burning coal that traps heat. You might picture machines that suck the gas in, new forests planted just for this, or crushed rock spread on fields so rain can lock the gas into stone. The other kind does not take the gas away at all. It tries to send a little of the sun's light back into space, so less heat lands on us: tiny bright dust high in the sky, or clouds over the sea made a bit brighter. Though actually, not all of this looks like “building a structure.” Some plans are more like spraying or planting at a giant scale. The word is fairly new and a bit slippery. Older talk sometimes used it for any huge earth-moving — dams, canals — but in climate talk now it almost always means these planet-scale cooling plans. It is a serious, formal word from news and science, not from the dinner table. Some people hate it because it sounds as if we can keep burning fuel and then “fix” the sky later. Others say we may need it if cutting fuel is too slow. You will hear both.