This is a yellow square. It is one of a variety of square emoji, representing yellow and dark yellow in the color. It is usually used to express colors more intuitively in conversations, and can also be combined with other emojis to express more specific meanings. Or you can put it at the beginning of a sentence as a bullet to make the text more eye-catching. Related emojis:
✨🌛 🌞 🟡 💛