What website is Shein?

Excuse me, could you possibly clarify for me what exactly is the website known as Shein? I've heard it mentioned in conversations about online shopping and fashion, but I'm not entirely sure what it offers or what sets it apart from other similar platforms. Is it a retailer specializing in a particular type of clothing or accessories? Or perhaps it offers a unique shopping experience or service? I'd really appreciate it if you could provide me with a concise description of the site and its main features.