Final answer:
The most effective medium for a short communication that requires a detailed explanation is an in-person meeting.
Step-by-step explanation:
If a communication is short, but requires a very detailed explanation, the most effective medium would be an in-person meeting. In this type of communication, you have the opportunity to have a face-to-face conversation and provide detailed explanations while observing the recipient's reactions and clarifying any doubts right away. It allows for a more interactive and comprehensive discussion, making it ideal for complex topics that require a thorough explanation.