A scenario can be used to create a different version of your budget.  Each scenario will use the same business configuration of your company (taxes, contribution, etc.) as well as the historical data. 

With scenarios, you will be able to forecast different situations like; 

- an optimistic version of your budget

- a pessimistic version of your budget

- the introduction of a new product

- expansion in a new market

- etc.

With the Enterprise plan you can have up to 5 different scenarios.  

See also: How to create a scenario.