Hinduism, like most religions, has many religious groupings. The Sanskrit word for this is sampradaya, which comes from the verbal root “da” meaning to “give.” A sampradaya therefore is something that is “given” or passed down from generation to generation. Hence, the idea of a religious tradition, a religious denomination or a religious sect. Each of these groupings fall within the idea of a sampradaya.
In general terms Hinduism breaks down into four broad groupings determined by which Deity is the major object of worship. There are Shaivas who focus on Shiva, Vaishnavas who revere Vishnu, Shaaktas who focus on a female form of Divinity, and many folk traditions. The expression “folk traditions” is a catchall phrase to mean the huge number of local traditions that pervade every part of Hinduism and which commonly intermix with the Shaiva, Vaishnava and Shaakta traditions. Each of these major groupings can be called a sampradaya, but even more so, within each of these major groupings there are many sub-groupings that can also be called sampradayas. Amongst the Shaivas, for example, there are Kashmiri Shaivas and Siddhanta Shaivas. Amongst the Vaishnavas there are Shri Vaishnavas, Madhva Vaishnavas, and Gaudiya Vaishnava, and many others. In this way, we can speak of each major grouping as a sampradaya as well as each sub-grouping as a sampradaya. If we compared this to Christianity, it would be somewhat similar to saying, Christianity is divided into three major groupings, Catholics, Orthodox and Protestants and within each of these major groupings are many sub-groups. Amongst Protestants, for example, there are Baptists, Methodists, Anglicans, Quakers, and so on. All of these major groupings and sub-groupings are the "sampradayas" of Christianity.
The Hindu idea of sampradaya is the closest thing to the idea of a religion in the traditional sense. Elsewhere we spoke of different models of religion, namely the tree and the river models. Hinduism we described as a river model and distinct from most other religions that follow a tree model of religion. The idea of the sampradaya is like a tree. Most of the sampradayas of Hinduism start from a source, a major philosopher or guru. Ramanuja is the founder of the Shri sampradaya of Vaishnavas, Madhva is the founder of Madhva Vaishnavas and so forth. Similarly Shankara is the founder of a major sampradaya of Hinduism called Advaita Vedanta. In this way Hinduism contains many religions within its scope.