It is the letter S rendered as the Unicode character ๐ (code point U+1D64E), part of the Sans Bold Italic styled alphabet. It is a single character you can copy and paste anywhere.
How do I type ๐ on my phone or computer?
You do not type it from a keyboard; you copy it. Press the copy button above and paste it into any app. That is the whole point of Unicode styled letters.
Where can I use the Sans Bold Italic S?
Anywhere text is accepted: Instagram bios, TikTok names, Discord, WhatsApp, gaming profiles and documents. The full Sans Bold Italic alphabet is linked above.