What is Strategic Business Unit?

Legal Definition
In business, a strategic business unit (SBU) is a profit center which focuses on product offering and market segment. SBUs typically have a discrete marketing plan, analysis of competition, and marketing campaign, even though they may be part of a larger business entity.

An SBU may be a business unit within a larger corporation, or it may be a business into itself or a branch. Corporations may be composed of multiple SBUs, each of which is responsible for its own profitability. General Electric is an example of a company with this sort of business organization. SBUs are able to affect most factors which influence their performance. Managed as separate businesses, they are responsible to a parent corporation. General Electric has 49 SBUs.

Companies today often use the word segmentation or division when referring to SBUs or an aggregation of SBUs that share such commonalities.
-- Wikipedia
Legal Definition
Strategic Business Unit or SBU is understood as a business unit within the overall corporate identity which is distinguishable from other business because it serves a defined external market where management can conduct strategic planning in relation to products and markets
Legal Definition
Organizational unit or autonomous division that is flexible and can exercise control over factors that effect long term performance.