In present Zoroastrian tradition, the word Gathas is used in two different but connected senses. The first is the name of a set of texts, and the other is the name of special days at the end of the Zoroastrian calendar year.
In the first sense, the Gathas are the sublime poetical compositions of prophet Zarathushtra in the oldest Avestan language. The word Gatha literally means “a song.” In the Gathas, we come across prophet Zarathushtra’s communications with Ahura Mazda, right from his quest for the Truth to his ultimate acceptance as the Prophet.
The 17 chapters of the Gathas are divided into five sections, totally comprising of 896 lines and about 5660 words, forming a part of the larger text of Yasna.
Each of the five Gathas are named after the first word of the first chapter of that group. The names of the five Gathas are: Ahunavad, Ushtavad, Spentomad, Vohu-khshathra and Vahishtoisht.
The Gathas are highly abstract, metaphysical and philosophical texts and hence very difficult to understand. Many translations of the Gathas are available, each differing somewhat from the other.
Several subjects are covered in the 17 chapters of the Gathas. As they are spread all over, no particular chapter covers any one topic in full. The subjects covered are about: Prophet Zarathushtra, Ahura Mazda, six attributes of Ahura Mazda (later known as Ameshaspands), two spirits, Immortality of the soul, Principle of Divine Justice, Maxims for Life, Manthra (prayers) and Rituals. Most of these topics are not dealt with in detail in Gathas. They are elaborated in later texts like the Vendidad. The Gathas also explain the essential Zoroastrian teachings, namely – Belief in One God, existence of the Spiritual world, existence of the two spirits or forces and belief in the immortality of the soul
The word Gatha is also used to denote the last five days of a Zoroastrian Calendar year, which form a part of the five Hamaspathmaedhem Gahambar days, and constitute the latter five days of the Muktad. These days were named after the 5 divisions of Gathas of prophet Zarathushtra, as these compositions were held in high esteem by Zoroastrians.