In South India and in Nepal, tiffin is generally an in between-meals snacks: dosas, idlis, etc. In other parts of India, such as Mumbai, the word mostly refers to a packed lunch of some sort, in particular to light lunches prepared for working men by their wives after they have left for work, or for schoolchildren by their parents. In Mumbai, it is often forwarded to them by dabbawalas, sometimes known as tiffin wallahs, who use a complex system to get thousands of tiffin-boxes to their destinations.
^OED staff 2013, "tiffin, n."cites H. Wedgwood (1862) "Tiffin, now naturalised among Anglo-Indians in the sense of luncheon, is the North country tiffing (properly sipping)". See also Wedgwood 1872, p. 682.