Reaction emoji
Replying to a message with a small emoji (👍❤️😂) instead of text. A lightweight response that confirms "seen/appreciated/heard" without filling the chat with "ok" messages. Nearly universal in modern apps.
Mechanic: hold/hover over a message and pick an emoji; it attaches to the message and tallies up if several people react. Apple calls its variant "Tapback". Win: it reduces noise (a thumbs-up instead of a separate "okay!" message), enables quick group polling (vote with emoji), and adds tone/feeling. In Slack/Discord, reactions become a working language of their own: ✅ for "done", 👀 for "looking at it", custom emoji for inside jokes. Scalable: a popular reaction can gather hundreds of clicks. One of the most widespread small UX patterns of all time. Related to custom emoji and group chat naming.