Denomination is a solution to a specific historical problem and it does not travel.
The problem was religious pluralism inside a single legal order. Once toleration made it impossible for one church to compel the others, English and then American Christianity had to describe an arrangement in which several bodies operated lawfully side by side, each governing itself, each holding that the others were mistaken about something, and none holding that the others had ceased to be Christian. The word denomination named that arrangement, and it carries all four assumptions with it: a countable membership, a self-governing polity, legal existence apart from the state, and mutual recognition across the boundary.
Apply it elsewhere and each of those assumptions fails.
A Hindu sampradaya is a line of transmission. It has teachers, texts, a preferred deity and a way of approaching that deity. It has no register, no boundary that must be crossed, no expulsion, and no expectation of exclusivity. A household routinely keeps a Vaishnava family deity, visits a Shiva temple and observes Navaratri for the Goddess without any sense of inconsistency. Another article in this collection makes the point at length and this entry follows it.
The madhhabs of Sunni Islam are methods of legal reasoning, not churches. A Muslim may follow the Shafii school, pray behind a Hanafi imam and take a Maliki opinion on a specific question, and nothing has been transgressed. There is no governing body and there is no membership.
Theravada, Mahayana and Vajrayana are not denominations either. They are different canons, lineages and practices, and monastic ordination lineages cut across them in ways that would make no sense if they were rival memberships.
This site files those traditions under a denomination heading because something has to hold them and because no better label has been agreed. That is a filing convenience. It is stated here rather than left for a reader to discover.