A chapel is a holy place or area of worship for Christians, which may be attached to an institution such as a large church, a college, a hospital, a palace, a prison or a cemetery, or may be free-standing and unattached to another building.
Architecturally, a chapel may be a part of a large church set aside for some specific use or purpose. In Roman Catholic Canon Law a chapel, technically called an "oratory" is a space dedicated to the celebration of services, particularly the Mass, which is not a parish church. This may be a private chapel, for the use of one person or a select group (a bishop's private chapel, or the chapel of a convent, for instance); a semi-public oratory, which is partially available to the general public (a seminary chapel that welcomes visitors to services, for instance); or a public oratory (for instance, a hospital or university chapel).
Chapel Wikipedia Entry