ABC is the three building blocks of WCF and they are known as,

 

A - Address (Where):- Address tells us where to find the services.

B - Binding (How):- Binding tells us how to find the services or using which protocols finds the services (SOAP, HTTP, TCP etc).

C - Contact (What):- Contract are an agreement between the consumer and the service providers that explains what parameters the service expects and what return values it gives.