The amnesia in Ghajini is anterograde amnesia, a condition where the ability to form new memories is impaired.
The protagonist, Sanjay Singhania, suffers from this condition due to a brutal attack that leaves him with severe head injuries.
He can only remember things for 15 minutes, making it incredibly difficult for him to function normally.
To compensate for his memory loss, he uses various methods like tattoos, photographs, and a complex system of notes to remind himself of important details and his mission for revenge.
This amnesia plays a key role in driving the plot, as Sanjay struggles to remember the events that led to his attack and to piece together clues about his attacker.