It refers to tourists in India who visit a place, but don't spend any money in the place they visit. They even carry their own food, mostly light snacks like Jhalmuri, hence they are referred to as "Jhalmuri Tourists".
Darjeeling is crowded these days with "Jhalmuri Tourists"
The term "Jhalmuri Tourist" refers to tourists who travel on a minimal budget, often using their own vehicles and avoiding expenditures at local restaurants by consuming their own food, typically light snacks such as Jhalmuri. This group isn't defined by a particular race, but by their style of travel and dining.
Hill stations are crowded these days, no thanks to the Jhalmuri tourists, who visit the place, use it's resources, without contributing to its economy.