S : The single-responsibility principle: "There should never be more than one reason for a class to change. In other words, every class should have only one responsibility."
O : The open–closed principle: "Software entities ... should be open for extension, but closed for modification."
L : The Liskov substitution principle: "Functions that use pointers or references to base classes must be able to use objects of derived classes without knowing it. See also design by contract."
I : The interface segregation principle: "Many client-specific interfaces are better than one general-purpose interface."
D : The dependency inversion principle: "Depend upon abstractions, [not] concretions."