FMBCS_S_HELD_LINES_KEY is a standard SAP Structure so does not store data like a database table does. It can be used to define the fields of other actual tables or to process "Key fields of table FMHBL (and of localization tables)" Information within sap ABAP programs. This is done by declaring abap internal tables, work areas or database tables based on this Structure. These can then be used to store and process the required data appropriately. i.e. DATA: wa_FMBCS_S_HELD_LINES_KEY TYPE FMBCS_S_HELD_LINES_KEY.
The FMBCS_S_HELD_LINES_KEY table consists of various fields, each holding specific information or linking keys about Key fields of table FMHBL (and of localization tables) data available in SAP. These include FM_AREA (Financial Management Area), CRTUSER (User Who Created or Updated the Object), DOCNR (Temporary Document Number (for Incomplete Documents )), DOCLN (Budget entry document line)... See below for full list along with technical details, documentation, text table, check tables, foreign key relationships, conversion routines, relevant tcodes and example ABAP select code etc. .