1. Rig Veda
2. Yajur Veda
3. Sama Veda
4. Atharva Veda
The Vedas are ancient texts that are sacred in India and renowned the world over. The world veda literally means knowledge. The root is vid, 'to know'. The Vedas are thus texts that provide knowledge.
There are four Vedas, known as the Rig Veda, the Yajur Veda, the Sama Veda and the Atharva Veda. Many years ago, the Vedas were referred to as trayi or three. There must have been some point of time when there were only three Vedas. These are acknowledged to have been the Rig Vedas, the Yajur Veda and the Sama Veda. The Atharva Veda is believed to have been a later addition to the sacred canon.
The world trayi is also interpreted in a different sense. Although the interpretation does seem to be slightly artificial, it is following. The three paths to salvation are believed to be those of jnana (knowledge), bhakti (devotion) and karma (action). Since the Vedas teach these three paths to salvation, they are referred to as trayi. The Rig Veda is identified with the path of knowledge, the Yajur Veda with the path of action, and the Sama Veda with the path of devotion.
Each of the Vedas has two parts, a samhita and the brahmanas. The samhita part consists of mantras or incantations. These were hymns that were used in sacrifies. But these mantras are difficult to interpret without commentaries. This is what the brahmanas set out to do. They explain the hymns and indicate how these are to be used in sacrifices. The brahmanas also have detailed descriptins of sacrifices and how they are to be conducted. The samhita and how they are to be conducted. The samhita and the brahmanas are often known as karma kanda, that is, the part of the vedas that deals with rituals.
In addition, Vedic literature also includes jnana kanda. This is the part that deals with supreme knowledge. Included in jnana kanda are the aranyakasf and the upanishads. These are identified with various Vedas.
We can therefore have a narrow definition of a Veda as well as a broad one. The narrow definition would take the word Veda to mean the samhita alone. The broad definition would include, in addition, associated brahmanas, aranyakas and upanishads. By the word Veda, we will mean the samhita alone.
When were the Vedas composed and who composed them? Strictly speaking, there is no answer to these questions. The Vedas were revealed; they were shrutis. They were not written down or composed. They were communicated by the supreme godhead or the divine essence (brahman) to the ancient seers (rishis). These rishis di not compose the Vedas; they merely obtained this divine knowledge through their extraordinary powers. In this sense, the Vedas are apourusheya, that is, not the handiwork of men. Their authorship cannot be ascribed to any human author.
In the Hindu conception of time, time is divided into four eras. These are known as satya yuga, treta yuga, dvapara yuga and kali yuga. As one moves from satya yuga towards kali yuga, the power of righteousness diminishes and evil starts to rear its ugly head. To bring men back to the righteous path, the sacred knowledge that is in the Vedas must ve disseminated amongst them. But the Vedas are abstract an esoteric, too difficult for ordinary mortals to comprehend. To make the dissemination and assimilation easier, the Vedas must be conveniently partitioned and divided into various groups. A person whos thus divides (vyasa) the Vedas has the title of Vedavyasa or Vyasadeva conferred on him.