That's the number that decides whether this breaker coordinates with your existing distribution gear, not just the motor full-load amps.
The 55 mm width means it takes up one standard modular slot — a detail the panel builder will appreciate when they're laying out the gland plate. Any mounting position works, so you're not forced into a specific orientation. Terminal screws are M6 for the main circuit, accepting up to 2x 35 mm² or 1x 50 mm² solid or stranded copper.
The interrupting rating drops as voltage climbs: 100 kA at 240 V, 50 kA at 400 V, 8 kA at 500 V, and 4 kA at 690 V. That's typical for a current-limiting breaker — the arc energy grows with voltage, so the same mechanism can't clear as much fault current. For a 480 V panel, the 50 kA at 400 V figure is the one to coordinate against; at 690 V you're down to 4 kA, which may force a larger upstream fuse if the available fault current is higher.