The Curve D trip characteristic means it tolerates higher inrush currents — typically needed for motor loads, transformers, or other inductive circuits where a standard Curve C would nuisance-trip on startup.
The single-pole format and DIN-rail clip mean it snaps into a standard 18 mm wide module slot in a distribution board or sub-panel. The 20 kA interrupting rating at 230/400 VAC gives it enough fault-clearing capacity for most commercial and light-industrial service-entrance panels. Keep the busbar arrangement clean — the single-pole breaker is often ganged with adjacent poles for multi-phase circuits, but each pole is a separate unit.