There is no difference between a Galah and a cockatoo.
A Galah IS a type of cockatoo.
The Galah is a unique cockatoo because it is the only species in its genus Eolophus.
This means taxonomists have decided that the Galah is different enough (often determined through DNA) to be in its very own grouping of cockatoos.
But it is still a cockatoo. Galahs are certainly physically unique when it comes to cockatoos – they are a rosy pink color on the front, part of the head, and under their wings.
The only other cockatoo in the wild with any pink coloring is the equally beautiful Major Mitchell’s Cockatoo – often simply also called the Pink Cockatoo. That species is lighter pink and has the most elaborate crest in the parrot world.