Icons are graphical representations used to symbolize actions, objects, or ideas. They are commonly used in user interfaces, websites, mobile apps, and presentations. Icons can convey meaning and provide visual cues to users. They come in different styles, such as flat icons, line icons, and glyph icons. Design principles like simplicity, clarity, and scalability are important when creating icons. Popular tools for designing icons include Adobe Illustrator, Sketch, and Figma. There are also online platforms that offer pre-designed icon sets, such as FontAwesome and Flaticon.