The CAP CER 3900PF 100V X7R 1808 is a specific type of ceramic capacitor. It has a capacitance value of 3900 pF, operates within a voltage range of 100V and belongs to the X7R category, which implies it can withstand temperatures from -55°C to +125°C. The metric code "4520" corresponds to the package size being an 1808 case.