A rule or policy that applies to everyone equally but ends up putting people with a particular protected characteristic, like age or sex, at a disadvantage. It’s unlawful under the Equality Act 2010 unless the employer can show it’s a proportionate way of achieving a genuine business aim.
In practice
If a venue shares tips mainly by length of service, that can indirectly discriminate against younger staff, since they're less likely to have long service through no fault of their own.
Legislation covered