What is the term for a program or mobile app that enables real-time communication among online users?

The correct answer is Instant Messaging, as this term specifically refers to a program or mobile app designed for real-time communication among online users. Instant messaging allows users to send text messages, share files, and often conduct voice or video calls instantly, facilitating immediate interaction.

Live Chat typically refers to a feature on a website that allows users to communicate with customer service representatives in real-time, but it is not generally a standalone program or mobile app aimed at general online users.

Video Conferencing involves face-to-face virtual meetings through video technology but is more complex than instant messaging, requiring more bandwidth and typically incorporating multiple participants and audio-video components.

Social Networking pertains to platforms that allow users to connect, share content, and interact with others but does not inherently emphasize real-time communication in the same way that instant messaging does. Social networks may include instant messaging features, but they encompass broader functionalities.