Kelantan–Pattani Malay is an Austronesian language of the Malayic subfamily spoken in the Malaysian state of Kelantan, as well as in Besut and Setiu districts of Terengganu state and the Perhentian Islands, and in the southernmost provinces of Thailand. It is the primary spoken language of Thai Malays and used as a lingua franca by ethnic Southern Thais in rural areas, Muslim and non-Muslim and the Sam-Sam, a mostly Thai-speaking population of mixed Malay and Thai ancestry.
Kelantan–Pattani Malay is highly divergent from other Malay varieties because of its geographical isolation from the rest of the Malay world by high mountains, deep rainforests and the Gulf of Thailand. It is also influenced by Thai in Thailand.
Kelantanese–Pattani Malay is distinct enough that radio broadcasts in Standard Malay cannot be understood easily by native speakers of Kelantan-Pattani Malay, such as those in Thailand, who are not taught the standard variety of the language. Unlike Malaysia, where Standard Malay is compulsory in the school curriculum, no one is required to learn Standard Malay in Thailand and so there is potentially less language influence from Standard Malay but potentially more from Thai. It is also distinct from Kedah Malay, Pahang Malay and Terengganu Malay, but those languages are much more closely related to the Kelantanese-Pattani Malay language than Standard Malay.