Polite past-tense expression of gratitude, used after someone has done something for you. More formal than ありがとうございます.
Thank you very much for all your help the other day.
ご来場いただき、ありがとうございました。
Thank you for coming.
ありがとう is the casual, everyday form used with friends or family, while 有難うございました is the formal past-tense version used in polite or business contexts.
Kanji spelling; it is a high-priority form.
Alternate kanji spelling with okurigana 有り難う.
From 有難う (ありがとう, 'thank you') + ございました, the polite past form of ござる ('to be'). Literally 'it was difficult to exist', expressing that the favor was rare and precious.