l-Kathulu-l
I seriously didn't realize the difference between Phys Atk and Spec Atk until about a week ago. I though Spec Atk referred to a pokemons type attack. Like Ampharos' Thunder. Elec and Elec. Not this move is categorized as special and your Spec Atk is...
Physical moves depend on how well a Pokemon's Attack stat is.
Special moves depend on how well a Pokemon's Sp. Attack stat is.
Here's an example:
Alakazam has two Psychic moves...Psycho Cut and Psychic. If it weren't for the phys/spec move split in gen 4, both of those moves would've relied on his Sp. Attack.
But each attack is now assigned specifically to be physical, special, or support. Psycho Cut is a physical move and Psychic is a Special move. So Psycho Cut relies on Attack and Psychic relies on Sp. Attack.
Alakazam's Attack stat is very, very low compared to his Sp. Attack stat. Therefore, Psychic will be much more useful than Psycho Cut, because it relies on an offensive stat Alakazam specializes in.
Gyarados on the other hand can learn Waterfall and Surf. Even though Surf has a higher base power, Waterfall will be much more usefull with Gyarados. That is because, as a result of the move split, Waterfall became a physical attack and Surf became a special attack. Gyarados' Attack stat far outclasses it's Sp. Attack stat, making Waterfall the better choice.