Centralisation is where a business Is controled from one head office.
For example. A business like Tesco's, instead of it being controled by a manager from seperate stores, It is controled by a big boss in one building.
Decentralisation Is where as a I said, a bussiness like Tesco's is controled by managers in every store but they still have to take orders from the main stem of the company.
Downsizing Is where one branch of the bussiness closes to keep profit and contend with other company's.
Flat organisational structure&Tall organisational
A Flat organisatinal structure is where a company has few layers of hirarchy so someone will have to line manage more people as alot of people are on the same level of hirarchy.
A Tall organisational structure is where the is a tall hierarchy and the preson above the hierarchy and the person above the other manages them.