A common snack in India, particularly Maharashtra; perhaps as prevalent in street food culture there as hot dog stands are on the streets of New York.
In short, the vada pav is a bit of batter-dipped, deep-fried mashed potatoes served on a bun (the "pav").
The mashed potatoes, strong with garlic, are dipped in chick pea batter, deep-fried, and served on the roll, often with chutney. The potatoes ("vada") may also be served as a snack on their own, without the pav.