In SAP and ABAP, a function module refers to a self-contained unit of code that performs a specific task or function. These modules are designed to be reusable and can be called from other parts of the program or from different programs altogether. Function modules are used to encapsulate business logic or perform specific operations within an SAP system. Some useful function modules are listed below. FICO: FTI_FISCAL_YEAR_MONTH_GET (To get Fiscal Year and Month) GET_CURRENT_YEAR(Getting current fiscal year) MM: /SPE/READ_CLASSIFICATION_DATA (Getting Batch Characteristics) PP: BAPI_PROCORD_CREATE (Process Order Creation) BAPI_REQIREMENTS_CREATE (PIR Creation) BAPI_REQUIREMENTS_CHANGE (PIR Change) CO_XT_COMPONENT_CHANGE (PP Order Component Change) CSAP_MAT_BOM_READ (BOM Read) AIP9_STATUS_READ (Order Status Read, OBJNR = OR + order) HCM: RKE_SELECT_FACTDAYS_FOR_PERIOD (Calculating Working Days) ABAP: ALSM_EXCEL_TO_INTERNAL_TABLE (Excel to Internal Table) RRBA_NUMBER_RANGE_RESET (Number