pitaya

Pitaya is just an alternate spelling of the more common pitahaya which is most commonly called dragon fruit (also strawberry pear).

The foodlywise website about dragon fruit explains health benefits of dragon fruit, how to grow dragon fruit and history of dragon fruit.

http://dragon.fruit.pitaya.fruit.foodlywise.com/

There is not difference other than the name between pitaya and pitahaya or dragon fruit.

Dragon fruit is just a common name for pitaya which is also called pitahaya or strawberry pear. There is no difference between the plant itself. There are just several names for the same plants.

The scientific name would be Selenicereus megalanthus.

Different cultivars of pitaya are red- or yellow-skinned; the internal part may be white or red.