)
From the tag description for "[dock":](https://www.derpibooru.org/tags/dock) : "The visible underside of a pony's tail where hair does not grow. Usually seen in rear views or with raised tails."
"Get" tags in general are meta tags, referencing the picture number on Derpibooru, rather than anything in the picture itself. So "palindrome get" applies to images where the number is a palindrome.