The Vedas (from the root vid, “to know,” or “divine knowledge”) are the most ancient of all the Hindu scriptures. There were originally three Vedas—the Laws of Manu always speaks of the three, as do the oldest (Mukhya) Upaniṣhads—but a later work called the Atharvaveda has been added to these, to now constitute the fourth. The name Ṛigveda signifies “Veda of verses,” from rig, a spoken stanza; Sāmaveda, the “Veda of chants,” from sāman, a song or chant; Yajurveda, the “Veda of sacrificial formulas,” from yajus, a sacrificial text. The Atharvaveda derives its name from the sage Atharvan, who is represented as a Prajāpati, the edlest son of Brahmā, and who is said to have been the first to institute the fire-sacrifices. The complex nature of the Vedas and the array of texts associated with them may be briefly outlined as follows:
“The Rig-Veda is the original work, the Yajur-Veda and Sama-Veda in their mantric portions are different arrangements of its hymns for special purposes. The Vedas are divided into two parts, the Mantra and Brahmana. The Mantra part is composed of suktas (hymns in verse); the Brahmana part consists of liturgical, ritualistic, exegetical, and mystic treatises in prose. The Mantra or verse portion is considered more ancient than the prose works; and the books in which the hymns are collected are called saṃhitās (collections). More or less closely connected with the Brahmanans (and in a few exceptional cases with the Mantra part) are two classes of treatises in prose and verse called Aranyaka and Upaniṣhad. The Vedic writings are again divided into two great divisions, exoteric and esoteric, the former called the karma-kanda (the section of works) and the latter the jnana-kanda (section of wisdom).” (Encyclopedic Theosophical Glossary)
Note: There are 13 Upanishads associated with or directly embedded within the Vedas and their Brahmanas and Aranyakas. These include the 10 Mukhya (“Principal”) Upanishads, plus three others. Because of this, some scholars consider all 13 to be Mukhya, though in the Muktika Canon, only the 10 are set apart.
See also: Vedāṅga, The Six “Limbs of the Veda”
Resources
Vedas: The Samhitas of the Rig, Yajur, Sama, and Atharva
Vedic Heritage Portal
The Vedas in Sanskrit
The Rigveda, Max Müller edition (Sanskrit) (Vol. 1, 2, 3, 4)
The Rigveda, Metrically Restored Text (Sanskrit)
Translations
Vedas: The Samhitas of the Rig, Yajur, Sama, and Atharva