According to the PMBOK® Guide, specifically within the Project Communications Management knowledge area, PMI distinguishes between two fundamental dimensions of successful communication: Effectiveness and Efficiency.

Effective Communication: This is defined as providing the information in the right format, at the right time, to the right audience, and with the right impact. The focus is on the quality and relevance of the communication to ensure the message is understood and achieves its intended purpose.

Efficient Communication: This refers to providing only the information that is needed. The focus here is on minimizing the waste of resources (such as time or budget) by avoiding " information overload " or sending unnecessary data.

Why the other options are incorrect:

A. Efficient: While a project manager should strive to be efficient, efficiency is about the quantity and resource usage (providing " only " what is needed). The specific criteria mentioned in the question (right audience, format, and time) are the literal definition of " Effective " communication in PMI standards.

C. Push: This is a Communication Method where information is sent to specific recipients who need to receive the information (e.g., emails, memos, reports). It does not guarantee that the information reached the right audience at the right time in the right format.

D. Pull: This is a Communication Method used for very large volumes of information or very large audiences. It requires the recipients to access the communication content at their own discretion (e.g., intranet sites, e-learning, lessons learned databases). Like push communication, it is a method, not a qualitative description like " effective. "