What are hidden abilities?

Question

I know the abilities are basically the Pokemon has another special ability but is there anything really special about those abilites?

Answer 1

Well other than being extremely hard to get a Pokemon with a hidden ability there is almost no difference. Some Pokemon have a hidden ability that is a regular ability on another Pokemon.

However sometimes the hidden ability is far superior to the normal ability. In how it works with the Pokemon and it's movepool and stats.

Answer 2

Available in Gen V, these Abilities are usually found through catching Dream World PKMN.
See here.