It's an instantaneous type (no time delay), designed for AC residual currents only, and built to snap onto a DIN rail in a standard distribution board — 3 modular width units wide, 70 mm deep.
The 40 A rating at AC is the continuous current it can carry in a 50 Hz circuit — sized for a sub-feed or a group of downstream breakers. The 30 mA trip threshold covers personnel protection (shock hazard) per IEC 60364. Because it's instantaneous, it trips within milliseconds on a fault, but that also means it's not suitable where you need a short time delay to ride through inrush or to coordinate with downstream RCDs. The insulation voltage is 460 V, and it withstands a 4 kV surge — overvoltage category III, so it's at home in the main distribution panel, not just sub-boards.
Temperature derating — the real-world current
Above that, it derates: 37.2 A at 45 °C, 36 A at 50 °C, 34.8 A at 55 °C, 34 A at 60 °C, 33.2 A at 65 °C, and 32 A at 70 °C. If your panel runs warm — say, a packed enclosure near a drive cabinet — the 32 A floor at 70 °C is the number to use for your load calculation.