The Linkage Section is used to define data items that are passed from a calling program.
General Format
LINKAGE SECTION. [ record-description ] ...
General Rules
1. Each level 01 and 77 data item described in Linkage must be uniquely named.
2. Subordinate data names need not be unique if they can be made unique through qualification.
3. Each level 01 and 77 data item declared in Linkage should be named in a USING phrase of the Procedure Division header. Data items that are REDEFINES of other data items should not be named, however.