The ABB S203P-K8 is a molded case circuit breaker (MCCB) from the S200 series, sitting in the Circuit Breakers, Fuses & Protection category. It's a current-production part, so you're not chasing an obsolete line item.
What it is and where it fits
Molded case circuit breakers like this one go into distribution panels and motor control centers to protect branch circuits against overloads and short circuits. The S203P-K8 is a three-pole unit, sized for DIN-rail mounting inside an enclosure — typical for a panel builder wiring up a sub-distribution board or a machine disconnect.