Casual income means an income which is casual in nature, i.e., which is unplanned, uncertain, accidental, sudden income which occurs just by chance and the person cannot depend upon it to produce income in future.
Example: Winning from lotteries, gambling, betting, etc.,
Apart from these, any incomes which are unanticipated and non-recurring in nature are called Casual incomes.
Similarly, capital gains, receipt from a business or an occupation and one-time benefits like bonus given to employees are not casual incomes.
As per Income Tax Act: Casual incomes upto Rs. 5000/- were exempt from tax but at present all casual incomes are subject to tax at 30% plus education cess (including surcharge, if any). They are treated as income from other sources and are taxable u/s 56 of Income Tax Act.