A puzzle that includes emoji in the question. Often, the goal of the puzzle involves deciphering their meaning.
Emoji (or emojis) are small cartoon-like images, commonly used to express an idea or emotion in mobile phone text communications or in chat messaging online.
Puzzles with this tag often require solvers to figure out a hidden meaning or message by interpreting various emoji and putting them into words.
The Emojipedia is a good reference for emoji-related material.