In Go, an interface is a collection of method signatures that a concrete type can implement. A concrete type is a defined type that has a specific underlying representation in memory.
Interfaces are used to define a set of behaviors that a type can exhibit without specifying its implementation details. Any type that implements the methods defined in an interface is said to satisfy that interface. This allows for polymorphism and abstraction, enabling different types to be used interchangeably if they satisfy the same interface.
On the other hand, concrete types are used to represent specific data structures and their associated behaviors. They have a fixed set of methods that are defined on the type itself. Concrete types are used to represent data structures and to implement the behavior specified by the methods defined on the type.
In summary, interfaces define a contract that a type can satisfy, while concrete types represent specific data structures and their associated behavior. Interfaces provide a way to abstract behavior and enable polymorphism, while concrete types provide the actual implementation of that behavior for a specific data structure.