What is Accounting Software?

Legal Definition
Accounting software describes a type of application software that records and processes accounting transactions within functional modules such as accounts payable, accounts receivable, payroll, and trial balance. It functions as an accounting information system. It may be developed in-house by the organization using it, may be purchased from a third party, or may be a combination of a third-party application software package with local modifications. Accounting software may be on-line based, accessed anywhere at any time with any device which is Internet enabled, or may be desktop based. It varies greatly in its complexity and cost.

The market has been undergoing considerable consolidation since the mid-1990s, with many suppliers ceasing to trade or being bought by larger groups.
-- Wikipedia
Legal Definition
Computer programs that aid in the keepign of accounting information like quickbooks.