A common Australian variety of cockatoo, scientific name Eulophus roseicapillus. It is pink with a dove-grey back, most of the body deep rose pink but the crown a soft pale pink: and very beautiful in an elegant, restrained way. It occurs in great flocks. The name is from the Yuwaalaraay language of northern New South Wales, is stressed on the final syllable, and is first recorded in 1862.
In Australian slang it is a gentle synonym for a dimwit, a numskull, a chucklehead, as in "The galah who takes me for an idiot's no fool".
The cockies or swagmen who roam the interior of Australia have a traditional recipe for the beautiful galah. (I learnt this from Alan Moorehead's book Cooper's Creek, the story of the Burke and Wills expedition.) You take the galah and an old boot and put them in your billy and boil them up until the boot is nice and tender, then you throw away the galah and eat the boot. (See cockatoo for another such recipe.)
Thanks to AnotherMartini for pointing out the Yuwaalaraay origin.