A belated return is an income tax return that you file after the original filing deadline (usually July 31st for most individuals) has already passed, but before a final, later cut-off date set by the tax department for that financial year, typically December 31st. Filing late doesn't mean you can't file at all — but it does come with consequences.
Filing a belated return usually attracts a late filing fee, and it can also mean losing certain benefits, such as the ability to carry forward some types of losses to offset against future income, which is only allowed if you file on time. Any tax refund you're owed can still be processed, but interest on delayed tax payments may also apply, so it's generally best to file well before the original deadline whenever possible.