This is a CAP CER 18PF 4KV C0G/NP0 1812 component. It has a capacitance of 18 pF and an operating voltage rating of 4000V or 4kV. The capacitor's dielectric material is Ceramic, specifically C0G/NP0 (1B) type. Its case size corresponds to the metric designation 4532, but it can also be referred to as an 1812 package in other contexts.