USAGE clause is mainly applicable to numeric data items in COBOL. It tells the form data is stored internally on the computer.
USAGE IS DISPALY COMP COMP-3
The USAGE clause may be used both in group item or an elementary item. If it is used in group item then it applies to all the items in that group
01 Table-1 usage is COMP. 05 item-1 pic $9(10). 05 item-5 pic $9(5).