The Body of Christ is a term used by Christians to describe believers in Christ. Christ is seen as the head of the body, which is seen as the church. The "members" of the body are seen as members of the church. The term may also be used (either symbolicly or literally) of the bread taken at communion.
In the context of the local churches it is a metaphor used to describe the synchronicity between different localities and God. In this, God is the head and the people who make up the Church in each locality are termed "members of the body". The "members of the body" may look different and/or may perform different functions, but they all work as one under the will of the head (God). For example, a person who is a gifted orator is encouraged to use his or her talents to act as a mouthpiece for God. Other such personal strengths would be similarly applied towards the "expression of Christ". In this way people can be functioning and active members of the "Body of Christ".