Tai Tham script is an abugida writing system used mainly for a group of Southwestern Tai languages i.e., Northern Thai, Tai Lü, Khün and Lao; as well as the liturgical languages of Buddhism i.e., Pali and Sanskrit. It is historically known as Tua Tham. In Thailand and Myanmar, the script is often referred to as Lanna script in relation to the historical kingdom of Lan Na situating in the Northern region of modern day Thailand and a part of Shan state in Myanmar. Local people in Northern Thailand also call the script as Tua Mueang in parallel to Kam Mueang, a local name for Northern Thai language. In Laos and Isan region of Thailand, a variation of Tai Tham script, often dubbed Lao Tham, is also known by the locals as To Tham Lao or Yuan script. Tai Tham script is traditionally written on a dried palm leaf as a palm-leaf manuscript.

An abugida – sometimes also called alphasyllabary, neosyllabary, or pseudo-alphabet – is a segmental writing system in which consonant–vowel sequences are written as units; each unit is based on a consonant letter, and vowel notation is secondary, similar to a diacritical mark. This contrasts with a full alphabet, in which vowels have status equal to consonants, and with an abjad, in which vowel marking is absent, partial, or optional – in less formal contexts, all three types of the script may be termed "alphabets". The terms also contrast them with a syllabary, in which a single symbol denotes the combination of one consonant and one vowel.