Tasks that have a financial cost and therefore can be posted against (debited from) accounts, for example, buying a new computer is a task that has a specified cost and needs to be posted against an account. Alternatively, as task such as calling a meeting has no cost and is considered non- billable.
Billable tasks can be tracked by their rates on an hourly basis. All billable tasks can be posted against certain accounts according to the posting criteria you set for each individual account.
Budget is a type of Account that represents a certain amount of money set aside by the organization or its individual departments to do business for a specific period of time, such as the fiscal year.