When something is controlled or regulated by many separate groups rather than one main group, it's decentralized. Many fast food chains are decentralized, with different franchises, owners, and managers spread across the world.
In many ways, the United States is decentralized. Although there is a central, federal government (with a president and congress that govern the entire country), many laws and regulations are decentralized, controlled separately by the individual states. In a decentralized business model, control and leadership are shared by many managers at different locations, instead of having one boss making all the rules.