CDISC-Gloss – The atomic unit of data transferred between systems. It comprises a group of segments in a defined sequence, each message has a message type that defines its purpose. NOTE: For example, the Admission, Discharge and Transfer (ADT) Message type is used to transmit portions of a patient’s ADT data from one system to another. in HL7, a three- character code contained within each message identifies its type. [HL7]