It's a disconnect switch for panel builders and line-side isolation — the kind of part you spec into a BOM when you need a manual, load-break disconnect that fits a standard DIN-rail or mounting-plate footprint.
Three poles means it switches all three phases of a 3-phase supply — standard for a motor disconnect or a feeder breaker in a control panel. The XT1S 125 TMF designation tells you it's rated for 125 A frame size with a thermal-magnetic trip.