Prior period errors are omissions from, and misstatements in, the entity’s financial statements for one or more prior periods arising from a failure to use, or misuse of, reliable information that:
(a) was available when financial statements for those periods were authorised for issue; and
(b) could reasonably be expected to have been obtained and taken into account in the preparation and presentation of those financial statements.
Such errors include the effects of mathematical mistakes, mistakes in applying accounting policies, oversights or misinterpretations of facts, and fraud.
Prior period errors are specifically discussed in IAS 8 Accounting Policies, Changes in Accounting Estimates and Errors.
Source: Glossary of Terms of IFRSs as at 31 December 2008.