This is a typical slight lunch from the Bristish India. It is called like this because of the English term: tiffing, which means little beverage. In the South of India and Nepal, this term is used to refer to a meal similar to a snack like the Indian dosas or idlis.
In general, this is used to refer to the habit of eating out of the scheduled hours. Tiffing is generally served in the dabba, which is a kind of metal container used to carry food (typical in Bombay).
Tiffins are usually sold during midday, or late in the afternoon. They are usually served with coffee (more common in the South). The tiffin sellers are called dabbawala.