This document defines key terms related to the assessment of income tax in India. It explains that an assessment is the procedure by which an assessee's income is determined by the Assessing Officer. An assessee refers to any person whose income or loss is assessed. A deemed assessee is one who is considered an assessee for another person, while an assessee in default fails to fulfill their duties under tax law. The document also defines person, assessment year, previous year, and outlines the various categories of residential status and their implications for tax incidence: resident and ordinarily resident, resident but not ordinarily resident, and non-resident.