The Greek noun alabastron (ἀλάβαστρον) refers to an alabaster flask — a small container of fine white stone used to hold precious ointments or perfumes. Such vessels were sealed at the neck and broken to release their contents.
A woman breaks an alabastron of pure, costly nard over Jesus — an act of extravagant, sacrificial worship He declared would be proclaimed throughout the world (Mark 14:9). True worship is costly and lavish. The broken jar is an image of total self-offering. What the world calls waste, the Lord calls beautiful.