It's a logo for the Apple iOS operating system. The middle of the logo are the letters "i" "O" and "S" where the "i" is lowercase and the "O" and "S" are both uppercase. The letters are placed inside of a square with rounded edges.
This iOS Logo icon is made in flat color style
. This format was developed by Icons8 designer team and became immensely popular for use in web and mobile applications. Feel free to download this icon in PNG format for free, or unlock other formats for $5. Unlike other icon packs that have merely hundreds of icons, this monster icon pack contains 5,900 icons, all in the same style and quality.