This indicates the file includes both the original English audio track and a professionally dubbed Hindi track, allowing viewers to switch between languages.
The specific version you referenced—"Dual Audio Hindi-DD51 480p"—highlights common technical specifications for digital releases in the Indian market: The Forever Purge 2021 Dual Audio Hindi-DD51 480p
Ana de la Reguera, Tenoch Huerta, Josh Lucas, Cassidy Freeman, Leven Rambin, Alejandro Edda, and Will Patton. This indicates the file includes both the original