Tattie is a potato. It is a Scottish word — you hear it in Scotland and in the north of England, in the kitchen, in the pub, on a menu in a small local place. It is warm and informal, the way a family word is warm. In standard English writing you would simply write 'potato'; if you see 'tattie' it is because the speaker is Scottish or is deliberately sounding Scottish. Two Scottish dishes carry it: 'mince and tatties' (minced beef with potatoes, a very ordinary home dinner) and 'tattie scone' (a flat potato cake fried for breakfast). You may also meet the same word spelt 'tatie' or 'tato' elsewhere.

馬鈴薯（蘇格蘭方言說法；台灣說「馬鈴薯」，不是中國的「土豆」——在台灣「土豆」是花生）