Notice
A notice is a formal communication from the FBR requiring you to do something, and it always states the section it is issued under and the deadline for compliance.
The section number determines everything: what is being asked, your rights, and the consequence of silence. Notices are served to your IRIS account, and service is effective whether or not you read it.
Related terms
IRIS
IRIS is the FBR's online portal where taxpayers register, file returns, receive notices and reply to them.
Best judgement assessment
A best judgement assessment under section 121 is an assessment the officer makes on his own estimate of your income, because you did not file or did not comply with a notice.
Section 111
Section 111 of the Income Tax Ordinance allows the FBR to treat any asset, expenditure or bank credit whose source you cannot explain as taxable income.