It means that they are rated to have 25A through their internal bus bar, and also though any wire-to-block connection point.
Note that these terminal blocks only have two screw connections; they are made to connect one single wire to another single wire. They also make jumper strips that connect in through the top of the terminal blocks. These either screw into place or simply press in:
On page 46 of the full datasheet, it says:
Jumpers carry 100% of rated terminal block current.
So let's do a thought experiment. Say you have 6 LED panels that take 5A each. You jumper six terminal blocks together (one for each panel), and you connect your power supply to one of these blocks. In this case, you have your main power wire providing 30A to one of the blocks, which isn't allowed by the ratings.
Instead, you could make two groups of three blocks each. That way you wouldn't have any single connection points that are over the rated current.
By the way, instead of buying the jumper strips you could just use wire to daisy-chain multiple blocks together. This requires multiple wires to be installed under the same screw clamp, which is not allowed by many industrial electrical codes.