(1) The number of a record that identifies the record within the source member.
(2) A field in a journal entry that contains a number assigned by the system. This number is initially 1 and is increased until the journal is changed or the sequence number is reset by the user.
(3) A 2-byte field in the structured field introducer that identifies the position of the structured field in the data set.
(4) A number assigned to each message exchanged between two nodes. The number is increased by one for each successive message. It starts from zero each time a new session is established.