Awadhi is an Indo-Aryan language. This language was spoken in a wide area including Lucknow and Ayoudhya (Awadh) earlier. Goswami Tulasidas wrote Ramcharitmanas, Geetavali, Kavitavali, and all his Shri Ram poems in this language.
Hindi is a much newer language mostly based on Awadhi and Braj Bhasha.