I meant to add a sentence to the page explaining so I'll do that soon.
The maximum is based on a nature that aids that stat. So the max attack number can only be reached if the pokemon has a Lonely/Adamant/Naughty/Brave nature. You also need max IVs, EVs and so on.
In the same way, the minimum is based on the nature hindering the stat, so for Attack you'd need to be Bold/Modest/Calm/Timid. You also need the lowest IVs, EVs and so on.
There is only one maximum and one minimum for each stat. Remember, the chances of getting the max/min are quite small, but they are useful as a guide. And you can't get the max in more than one stat because of the nature thing.
If you manage to get remotely close to the max then your pokemon will be very strong in that stat!