Milk left over heat passes through several usable states before it dries out entirely. Indian sweet-making names those states and treats them as distinct ingredients rather than as stages of one thing.
Reduction changes proportion, not composition
Whole milk is mostly water. As that water leaves, fat, protein and lactose stay behind, and their share of the remaining mass climbs steadily with every minute of boiling.
Early in the process the liquid simply thickens and tastes richer. Past a certain point the sugars begin to brown and the flavor shifts from milky toward caramel and nuts.
Because texture and flavor move together, stopping at different points gives genuinely different ingredients rather than thicker and thinner versions of a single one.
The early stages stay pourable and get used as sauces
Milk reduced by roughly a third is still fluid. It coats a spoon, sweetens easily and forms the base of the poured and set desserts that are served in bowls.
Reduced further it turns into a heavy, spoonable cream that clings rather than pours. This is the stage layered over breads and folded through nut mixtures.
Neither stage will hold a shape on a plate. Anything that requires a cut edge has to be taken considerably further than this.
The late stages become a dough-like solid
Continue reducing and the mass stops flowing altogether. It pulls away from the pan in a single lump and can then be pressed, rolled or grated.
How it is stirred at this point decides the final grain. Constant stirring keeps the lactose in fine crystals and the texture smooth; less stirring leaves coarser grains that read as sandy.
Both results are wanted, for different sweets. A smooth solid is shaped into slabs and cut, while a grainy one is used where a slight crumble is the whole point.
Speed matters as much as duration
Fast reduction over high heat browns the milk sugars before enough water has left, giving a dark, faintly bitter product that is thin for how deep its color looks.
Slow reduction in a wide, heavy pan lets water escape faster than browning progresses. The result stays pale and sweet even after a long stretch on the stove.
An American stove changes the calculation
Wide pans and a large burner speed evaporation, because surface area rather than flame size governs how quickly water leaves. A tall stockpot is the wrong shape for this job.
Cooks working with a small electric coil often reduce in batches in a skillet instead, which trades more pan-watching for a shorter total time and much less risk of scorching.