The D-curve means it's designed to handle high inrush currents — think motor starts, transformer energization, or capacitive loads — without nuisance tripping on the initial surge. For a 2 A rating, that's typically protecting a small motor circuit or a control transformer secondary where the startup spike would blow a B-curve breaker.
The 6 kA breaking capacity at 230 V covers the majority of domestic and small commercial fault levels; if your site has a higher prospective short-circuit current (say, 10 kA or more at the panel), you'd step up to the 5SL7 series with a 10 kA rating.