S.O.L.I.D is an acronym for the first five object-oriented design(OOD) principles by Robert C. Martin, popularly known as Uncle Bob.
S stands for SRP (Single responsibility principle
O stands for OCP (Open closed principle)
L stands for LSP (Liskov substitution principle)
I stands for ISP ( Interface segregation principle)
D stands for DIP ( Dependency inversion principle)