Adat is a generic term derived from Arabic to describe a variety of local customary practices and traditions deemed compatible with Islam as observed by Muslim communities in the Balkans, North Caucasus, Central Asia, and Southeast Asia. Despite its Arabic origin, the term adat resonates deeply throughout Maritime Southeast Asia, where due to colonial influence, its usage has been systematically institutionalised into various non-Muslim communities. Within the region, the term refers, in a broader sense, to the customary norms, rules, interdictions, and injunctions that guide individuals' conduct as members of the community and the sanctions and forms of address by which these norms and rules are upheld. Adat also includes the set of local and traditional laws and dispute resolution systems by which these societies are regulated.

Undang-Undang Melaka, also known as Hukum Kanun Melaka, Undang-Undang Darat Melaka and Risalah Hukum Kanun, was the legal code of Melaka Sultanate (1400–1511). It contains significant provisions that reaffirmed the primacy of Malay customary law or adat, while at the same time accommodating and assimilating Islamic principles. The legal code is believed originally compiled during the reign of Muhammad Shah (1424–1444), before it was continuously expanded and improved by the succeeding sultans. The Melaka system of justice as enshrined in the Undang-Undang Melaka was the first digest of laws, compiled in the Malay world. It became a legal resource for other major regional sultanates like Johor, Perak, Brunei, Pattani and Aceh, and has been regarded as the most important of Malay legal digests.