Purity is the quality or state of being pure. In science and shopping, that usually means how much of a thing is only itself: gold of high purity has little other metal in it; water purity is about dirt and chemicals. In morals and religion, purity is about a clean heart or clean behaviour, and people often tie it to sex — purity rings, talks about “keeping pure.” That moral use can feel heavy or old-fashioned, and some younger people push back against it. You also hear it for ideas: purity of intention (you meant only that), or the purity of a colour or a note (nothing mixed in). Same English word; the Chinese often splits. The core picture is the same: nothing extra, nothing staining it.