http://help.sap.com/saphelp_sapcloudforcustomer/en/PDF/EN-1.pdf
SAP Help 3.14
Hi, best definition I found (not on SAP pages) is...
'Best Case' - includes amounts that you are likely to close/win
'Commit' - includes amounts that you are confident of winning/closing
'Pipeline' - - includes amounts from all open opportunities.
Regards Wendy Cushley