For most Hindus, their belief and practice is a loosely defined spiritual philosophy, however, the core foundation of Hinduism, The Vedas, is very specific about the nature of God as an overarching principle encompassing all other concepts of Divinity. Most Hindus would rather simplify their spiritual life by focussing their devotions upon one, or perhaps two or three particular deities and self-identify as members of one or more of the four main sects within Hinduism.
Shaivism, where Shiva is worshipped as the Supreme Deity in the sense that other gods and goddesses are manifestations of Shiva. Shaivism was the dominant sect in the Chola Period and remains so in south India today,
Vaishnavism dominates within Hinduism overall with some 70% of Hindus believing that Vishnu, or one of his iterations such as Krishna, is Supreme over all other gods,
Shaktism holds the female aspects of God as Supreme. While certainly a minority it’s followers are no less devoted to Shakti in all her manifestations, such as Uma, Kali or Saraswati,
Smartism generally rejects the sectarian belief in one god above all. It holds to a Vedic belief that the six primary gods of Hinduism; Shiva, Vishnu, Shakti, Ganesh, Murugan and Surya (the Vedic Sun god) manifest the formless Brahman more or less equally.
True to the pluralist and inclusive nature of Hinduism, each sect’s followers freely borrow beliefs and practices from each other.
“Brahman is the One, the One alone, in Brahman all deities become One alone.”
The Artharva Veda
Other sects may venerate less popular deities such as Krishna, Murugan or Ganesha, but do so with the fervour and dedication of the major sects. If such a group, or sect, has a defined philosophy and led by a particular guru, it is said to be sampradaya. An example would be The International Society for Krishna Consciousness (ISKCON), commonly referred to as the Hare Krishna movement, formed in 1966 by A.C. Bhaktivedanta Swami Prabhupada.