As basis you are sometimes confronted with special requests. For these special requests, you will need to know for part SAP uses which tables so you can use SE16N for internal lookup of information.
The below is a list of tables used in SAP basis.
Disclaimer 1: table list is not complete.
Disclaimer 2: tables can change each SAP version.
SAP mail / SCOT
BCSD_BLMODULE
BCSD_BREAKLOOP
BCSD_RQST
BCSD_STML
SXADMINTAB
SXCONVERT
SXCONVERT2
SXCOS
SXCOS_T
SXCPDEF
SXCPRECV
SXCPSEND
SXDEVTYPE
SXDEVTYPL
SXDOMAINS
SXJOBS
SXNODES
SXPARAMS
SXRETRY
SXROUTE
SXSERV
SXTELMOIN
SXTELMOOUT
USMM user management
TUAB_ANNOTATION
TUAB_WF_TYPE
TUAB_WF_TYPE_T
TUAPP
TUAPPT
TUAPUSG
TUCON
TUGRP
TUJOB
TUL_AC_UNIT
TUL_AC_UNITT
TUL_ACRES
TUL_ACTTC
TUL_CLIENTS
TUL_CONTROL
TUL_CPU
TUL_CPU_RAW
TUL_ENG_PL
TUL_ENG_PROT
TUL_ENG_RESULT
TUL_ENG_RESULT_1
TUL_ENGINES
TUL_ENGINEST
TUL_JOB
TUL_MEMOS
TUL_MSG
TUL_TRANS
TUL_TRSTAT
TUL_UNIT
TUL_UNITT
TULAPP_PL
TULTRANS
TUMRES
TUMSG
TUPL
TUPLT
TUPRO
TUSERSETTING
TUSERSETTINGPROD
TUSTAT
TUTYHLP
TUTYP
TUTYPA
TUTYPASYS
TUTYPNOWSYS
TUTYPP
TUTYPPL
TUZUSSYS
STMS transports and settings
TMSBCIBOX
TMSBCIIBOX
TMSBCIJOY
TMSBCINEX
TMSBCINTAB
TMSBCIOBJ
TMSBCIXBOX
TMSCDES
TMSCDES_S
TMSCDESD
TMSCDIST
TMSCDOL
TMSCDOM
TMSCDOMT
TMSCNFS
TMSCNFST
TMSCROUTE
TMSCSYS
TMSCSYST
TMSCTOK
TMSFSYSH
TMSFSYSL
TMSMCONF
TMSPCONF
TMSPVERS
TMSSRV
TMSTCRI
TMSTLOCKP
TMSTLOCKR
TMSTOUT
TMSUCONF
E070L
E071
E071K
STMS History
TMSQLASTWL
TMSQNOTES
TMSQNOTESH
TMSQWL
TMSQWLF
TMSQWLFH
TMSQWLH
Database connections
DBCON
DBCONUSR
Files
FILENAME
FILENAMECI
FILEPATH
FILESYS
FILETEXT
FILETEXTCI
OPSYSTEM
OPTEXT
PARAMVALUE
PATH
PATHTEXT
USER_DIR
STRUST settings
SSF_PSE_D
SSF_PSE_H
SSF_PSE_T
SSFAPPLICT
SSFARGS
STRUSTCAB
STRUSTCERT
STRUSTCRL
STRUSTCRP
STRUSTCRPT
STRUSTCRR
STRUSTCRRT
STRUSTCRS
STRUSTCRT
STRUSTSSL
STRUSTSSLT
STRUSTWSSE
STRUSTWSSET
TWPSSO2ACL
USERINFO_STORAGE
USRACLEXT
USRCERTMAP
USRCERTRULE
Content server and SAP DMS settings
CREP_FTP
CREP_RPC
CREP
CREP_FILE
CREP_HTTP
CREP_LREP
CREP_R3DB
CREP_RFC
CREP_TREE
CREPDESCR
CREPDOCSP
SWU3 workflow settings
SWFGPACTIVITIES
SWFGPCONF
SWFGPDEPLOY
SWFGPGENOBJNUM
SWFGPREUSE
SWFGPROLEDEF
SWFGPROLEINST
SWFGPWULACDEF
SWFGPWULDATOBJ
SWFGPWULFLOWS
SWFGPWULTASKS
Classic TVARV
TVARUVN
TVARV
TVARVC
SICF nodes
ICF_SESSION_CNTL
ICFALIAS
ICFAPPLICATION
ICFBUFFER
ICFDELTA
ICFDOCU
ICFHANDLER
ICFHANDTREE
ICFIMPORT
ICFINSTACT
ICFLOGORDER
ICFNOHANLDER
ICFSECPASSWD
ICFSERVICE
ICFSERVLOC
ICFVIRHOST
Start menu settings
SSM_CUST
Webservices logical ports & soap runtime
SRT_LP
SRT_LP_FEAT
SRT_LP_OP_FEAT
SRT_LP_SXI_ADDR
SRT_LP_T
SPROXMSGREL
SRT_SLT_HOSTS
SRT_ASSIGN_DATA
SRT_ASSIGN_DIR
SRT_ASSIGN_DIR_T
SRT_AU_TEST_RECI
SRT_CACHE
SRT_CC_CHANGES
SRT_CC_CHANGES_H
SRT_CC_MIF_CDATA
SRT_CC_MIF_CDIR
SRT_CC_MIF_LDATA
SRT_CC_PC
SRT_CC_PP
SRT_CC_ST_ACT
SRT_CSTC
SRT_CDTC_C_DET
SRT_CDTC_CHD_ID
SRT_CDTC_DESCR_T
SRT_CDTC_G_DET
SRT_CDTC_S_DET
SRT_CFG_BNDG
SRT_CFG_CFGVAL
SRT_CFG_CHG_TAB
SRT_CFG_CLI_ASGN
SRT_CFG_DATA
SRT_CFG_DEF_ASGN
SRT_CFG_DIR
SRT_CFG_DIR_T
SRT_CFG_ICF_DET
SRT_CGF_ICF_USE
SRT_CFG_LOG_HDR
SRT_CFG_LOG_ITEM
SRT_CFG_LOG_SRCH
SRT_CFG_MLP_DATA
SRT_CFG_SRV_ASGN
SRT_CFG_STS_ASGN
SRT_CFG_SV_ASN_T
SRT_CFG_TPLC_DAT
SRT_CFG_TPLC_DIR
SRT_CFG_TRC
SRT_CFG_TRC_ADM
SRT_CFG_VAL_DET
SRT_CFG_VAL_DIR
SRT_CFG_VAL_UPD
SRT_CFG_VALUES
SRT_CG_SYST_ATTR
SRT_CG_SYST_DIR
SRT_CG_WSDL_CONT
SRT_CG_WSDL_URL
SRT_CHECK_HEADER
SRT_CHECK_RESULT
SRT_CHECK_STATUS
SRT_CLI_NR
SRT_CNTRL_TASKS
SRT_CON_SYSTEMS
SRT_CTRL_TSK_MSG
SRT_DEST_CFGV
SRT_DEST_DATA
SRT_DEST_DIR
SRT_DEST_DIR_T
SRT_DEST_DIR_V
SRT_DEST_WSDL
SRT_DOMAIN_SYS
SRT_DOMAIN_SYS_T
SRT_DOMN_DIR
SRT_DOMN_DIR_T
SRT_DOMN_SYSTS
SRT_DT_CFG_DATA
SRT_DT_CFG_DIR
SRT_DT_CFG_DIR_T
SRT_DT_CHG_DIR
SRT_DT_CHG_DIR_L
SRT_DT_CHG_STAT
SRT_DT_CHG_STATL
SRT_FALLBACK_LPS
SRT_FW_SETTINGS
SRT_GEN_CLNT_DIR
SRT_IDENTIFIER
SRT_ISO_SET_C
SRT_ISO_SET_P
SRT_LOG_TENANT
SRT_LOG_TENANT_R
SRT_LP
SRT_LP_FEAT
SRT_LP_OP_FEAT
SRT_LP_SXI_ADDR
SRT_LP_T
SRT_LP_URL_ASGN
SRT_LRD_HEADER
SRT_LRD_ROUTING
SRT_MED_SYS
SRT_MED_SYS_T
SRT_MIG_HIST
SRT_NAME_CACHE
SRT_OBSERV_DATA
SRT_PEND_TASK
SRT_PRF_CFG_DIR
SRT_PRF_CFGVAL
SRT_PRF_DATA
SRT_PRF_DIR
SRT_PRE_DIR_T
SRT_PRE_DIR_V
SRT_PRO_WKL
SRT_PROF_ASSIGN
SRT_PRULE_ASSIGN
SRT_PRULE_DATA
SRT_PRULE_DIR
SRT_PRX_CLNT_DIR
SRT_PRX_EX_CHECK
SRT_PT_INDEX
SRT_PX_MSG_ASGN
SRT_REG_ADRMAP
SRT_REG_BACKUPR
SRT_REG_BIND
SRT_REG_CONFIG
SRT_REG_OPERAT
SRT_REGISTRY
SRT_REGISTRYT
SRT_REQ_DATA_C
SRT_REQ_DATA_CON
SRT_REQ_DATA_P
SRT_REQ_DATA_PIF
SRT_REQ_DATA_PRO
SRT_REQ_DIR
SRT_REQ_DIR_T
SRT_REV_PROXY
SRT_RTC_BNDG
SRT_RTC_CFGVAL
SRT_RTC_CG_DATA
SRT_RTC_CG_DATAL
SRT_RTC_CG_DIR
SRT_RTC_DATA
SRT_RTC_DATA_RT
SRT_RTC_DATAL
SRT_RTC_DIR
SRT_RTC_DT_IF_SD
SRT_RTC_DT_RT
SRT_RTC_DT_RT_MD
SRT_RTC_WSIL
SRT_RTC_WSILL
SRT_SAVED_SEARCH
SRT_SCP_ASSIGN
SRT_SDN_URL_C
SRT_SECSTORE_LNK
SRT_SOAM_CONNECT
SRT_SR_CLASS_S_T
SRT_SR_CLASS_SYS
SRT_SR_CLASS_V_T
SRT_SR_CLASS_VAL
SRT_SR_SEP
SRT_SR_SEP_T
SRT_SR_SYSTEM
SRT_SR_UDDI_ROW
SRT_SR_VW_ASSIGN
SRT_SR_VM_DETAIL
SRT_SR_VM_HEADER
SRT_SR_WSD
SRT_SR_WSD_T
SRT_ST_ACT_A
SRT_ST_ACT_C
SRT_ST_ACT_C_C
SRT_ST_ACT_P
SRT_ST_ACT_P_C
SRT_ST_REQ_A
SRT_ST_REQ_C
SRT_ST_REQ_P
SRT_SYS_NR
SRT_SYS_SETTINGS
SRT_SYST_APPL
SRT_SYST_APPL_HT
SRT_SYST_CL_DATA
SRT_SYST_CL_DIR
SRT_SYSTEM_DIR
SRT_TEST_CONCATE
SRT_TMP_CG_DATA
SRT_TMP_CG_DATAL
SRT_TRACE_USERS
SRT_TRANSP
SRT_TRANSP_A
SRT_TRANSP_KEYS
SRT_TRC_ASSIGN
SRT_TRC_COUNTER
SRT_TRC_FILES
SRT_U_ASSIGN_DAT
SRT_U_ASSIGN_DIR
SRT_UASSIGN_DIR
SRT_USER_DATA
SRT_USER_DIR
SRT_USER_DIR_T
SRT_WHITE_LIST
SRT_WSDL_CACHE_P
SRT_WSDL_DIR
SRT_WSDL_DIR_T
SRT_WSDL_DS_ASGN
SRT_WSDL_ENTITY
SRT_WSIL_CACHE_C
SRT_WSIL_CACHE_P
SRT_WSIL_TMP
SRT_WSP_WSDL_FLA
SRTFT_ASSIGN
SRTFT_ASSIGN_IF
SRTFT_ASSIGN_SEC
SRTFT_NM_CFG_MAP
SRTFT_QDATA_LOG
SRTFT_QUEUE
SRTFT_QUEUE_DATA
SRTFT_QUEUE_LG_T
SRTFT_QUEUE_LOG
Content server settings
CREP_FTP
CREP_RPC
CREP
CREP_FILE
CREP_HTTP
CREP_LREP
CREP_R3DB
CREP_RFC
CREP_TREE
CREPDESCR
CREPDOCSP
Idoc settings WE20, WE21
EDMA
EDP12
EDP13
EDP21
EDPP1
EDIPO
EDIPO2
EDIPOA
EDIPOD
EDIPOF
EDIPOI
EDIPORT
EDIPOX
EDIPOXH
SAP license key
SAPLIKEY
OS commands SM49, SM69
SXPGCOSTAB
SXPGCOTABE
SXPGHISTOR
SNC
SNCSYSACL
TXCOMSECU
USRACL
TSP0U
RFC’s SM59
RFCTA
RFCTYPE
RFCLIST
RFC_TT_ACL
RFCATTRIB
RFCCBWHITELIST
RFCCHECK
RFCCMC
RFCDES
RFCDESSECU
RFCDOC
RFCGO
RFCSTXTAB
RFCSYSACL
RFCSYSACL_CLNT
RFCTRUST
ALE distribution model BD64
TBDLI
TBDLS
TBDLST
TBDLT
TBDBR
TBDBRF
TBDA2
TBD00
TBD00T
TBD03
TBD05
TBD06
TBD20
TBD30
TBDTPBDF
TBDTPBR
TBDTPMD
TBLSYSDEST
TBSPECDEST
ALV grids
LTDX
LTDXD
LTDXT
Secstore
RSECACHK
RSECACTB
RSECSESSION_CL
RSECTAB
RSECVAL
RSECVAL_CL
Spools and printers
TSP03
TSP03A
TSP03C
TSP03D
TSP03L
TSP03POCCNF
TSP03POCPRE
TSP03T
TSPCMDS
TSPLOMS
TSPROMS
TSPSV