Assessment includes reassessment under income tax law, clarifying scope of taxable scrutiny and procedural reach. Assessment as a defined term in income tax law encompasses reassessment, extending the statutory concept to include subsequent review or re-evaluation of tax liability. This definition frames the procedural ambit for initiating further inquiries or adjustments after an initial assessment. Manuals, ready reckoners, quick commentaries and reference guides are identified as practice tools to assist interpretation and administration but do not substitute for statutory definition.