A long, thin, chocolate-covered cookie popular in Japan similar to a biscotti. There are other Pocky flavors that are shipped throughout the world. In Europe it is available under the name Mikado.
Thanks to its immense popularity amongst the Japanese and elsewhere, it has been featured in a number of anime, such as Please! Teacher, Please! Twins, X/1999, etc. Due to copyright issues, it is nearly always mentioned under a different name, usually a mangled pronunciation, misspelling, or homonym, such as Pooky, Pochy, Rocky, et. al.
November 11 is Pocky Day, because the shape of resembles the numeral 1.
Danbooru does not distinguish Pocky from Pepero (빼빼로), a Korean version of Pocky.