What is 'block booking', which Bollywood is accused of doing?

Block booking happens when a producer or actor pays for multiple seats to create positive perception around the film. Describing 'corporate booking', trade expert Atul Mohan said, "If an actor endorses 20 brands, they ask one brand to, for example, purchase 10,000 tickets...In return, they waive off some fees, or shoot ad for free." Bollywood is facing several such allegations.