Financial Year
It is a period which start from 1st April & end on 31st March. It is the year in which the taxpayer earned the Income.
As per Income tax Act – It is known as a Previous Year
Assessment Year
Assessment year (AY) is the year following the financial year, in which your income is assessed. This also lasts from 1 April to 31 March and is the year in which you file your income tax returns for the taxes paid in the relevant financial.