A bare root plant is a plant that is sold with the roots exposed, rather than in soil.
Not all types of plants can handle being shipped this way. However, for those that can, such as roses, fruit trees and shrubs and several perennials including hosta and daylilies, it is perfectly acceptable.
Plants sold bare root are dormant and should be planted ASAP. The roots should be kept moist at all times while exposed.
Examples: When my raspberry canes came in the mail they were shipped bare root and looked more like dead sticks than berry bushes.