This is a ceramic capacitor with the designation CAP CER 91PF 1KV NP0 1808. It has a capacitance of 91 pF ±10 and can withstand a voltage of 1000V (1kV). The capacitor is classified as C0G, also known as NP0, which is a type of ceramic dielectric material that exhibits low temperature coefficient of capacitance and high stability over time.