Bare root is an old fashioned way to sell plants i.e. before it became easier to grow and distribute them in plastic pots. When the plant is dormant in spring or autumn it can be lifted from the ground with some soil and will survive for a few days if kept moist e.g. wrapped in wet newspaper.
 A few growers still follow this practice. Most years I place an order with a nursery in Wales who raise wildflowers and bulbs on their smallholding. I reckon they are about as close as you get to actual wild plants. Many garden centres now sell a range of wildflowers grown in plastic but I find them to be fairly tender whereas these are tough as old boots. I think the roots establish better too because they have not become 'potbound'.
 I bought some Columbine for the garden (above) and various sun loving plants for a bed on the allotment: Meadow Cranesbill, Field Scabious, Greater Knapweed etc. Also some Soloman's Seal for a shadier spot and Yellow Flag Iris for the pond.