Auditing Query CA Final

Hello

Can anybody help me in this,
What is the meaning of assertion,as it is used in auditing book again and again, but i dont know what exactly is assertion in the terms of audit, as used in chapter 2 in study material CA Final, under heading Formulating an audit programme, i.e. Assisstants should be able to identify the assertions made in the Balance Sheet and Profit & Loss Account because that provides key to the auditor's selection of the procedures.

Waiting for the reply