In the context of the word Pannier being used for the term "Pannier Market", this indicates a Fruit and Vegetable market. Although the Tavistock Pannier Market has diversified over the years they still maintain the traditional Charter every Friday which includes fruit and vegetable stalls.
A Pannier is also one of a pair of baskets worn by a beast of burden
OR can be a pair of baskets fixed on either side of a bicycle.
Pannier - One of a pair of baskets