To define Business group, LE, OU, Organization, HR Organization etc check out below link
SOB is a sepcial organization in multi-org model. Its a financial entity that shares a particular hart of account, finctional currency and finncial accounting calendar. A General Ledger (GL) secures transaction information bu SOB.
An SOB is the highest level that affects the accounting aspects of business. One BG can be associated with multiple SOBs, but one SOB can be associated with only one BG. Each SOB has 3Cs.
With the multi-Org enhancements, multiple SOBs can use the same global item master organization. This is because the item master organization is used for item definition and not for item accounting information. All accouting-related attributes in the item master are controlled at the item level or organization level.