Interface Segregation
In plain terms
Clients shouldn't depend on methods they don't use.
Going deeper
The Interface Segregation Principle favors many small, specific interfaces over one large general one, so implementers aren't forced to support irrelevant methods. Keep interfaces focused.
Under the hood
The 'I' in SOLID; reduces coupling and avoids fat interfaces with unused obligations.
Examples
SOLID, focused interfaces, decoupling, role interfaces, lean contracts.
Think of it like...
Like ordering à la carte instead of being forced to buy a giant fixed menu.