Interpersonal interaction is the process in which messages, feelings and information are conveyed, this could be via verbal communication or non-verbal communication, between two or more people. In order to classify it as interpersonal interaction it must occur face to face.
Effective communication is when the message you want to convey is delivered, received and understood by the person or people the message was aimed at. The messages could be delivered through verbal communication or other methods, such as written communication or non-verbal communication, without being misunderstood. However, effective communication is not just about relaying messages successfully but also about being able to understand the reasoning and intentions as well as the emotions behind the message and information that is relayed.