A Business Continuity Plan describes a set of procedures your company will use to continue critical business operations in the event of disruption (of that specific and/or all critical business operations). For instance, if the ability to take phone calls is a critical business operation (i.e. maybe you run a help desk), then you may define, in your BCP, what may cause a phone interruption, and what procedures you would take to respond to it.
Conversely, as stated by Massimo, the Disaster Recovery Plan (DRP) is a subset of your BCP. The DRP specifies the further reaching implications of disaster -- where your primary place (or all places) of business are uninhabitable. Not only is this relevant to your place of business, but your workforce as well (Workforce Continuity).
Several organizations often combine the concept of both, calling it a BCDR (Business Continuity / Disaster Recover) plan. This is what we've done.