The ABB XT4SU3250BFF000XXX is a 1-pole molded case circuit breaker from the XT4S family, fitted with a TMA trip unit rated 250 A with an adjustable overload range of 1250-2500 A. It is a wall-mount unit, so it lands on a backplate or enclosure wall rather than a DIN rail — factor that into your panel layout and gland-plate planning.
The single-pole construction (1-pole) means this breaker switches one phase only — typical for a single-phase branch circuit or a DC application where only one ungrounded conductor needs protection. It is not a 3-pole device; if your BOM calls for three-phase switching, this is the wrong pole count.