OpenSea is a marketplace for digital goods, including collectibles, gaming items, digital art, and other digital assets that are backed by a blockchain like Ethereum. On OpenSea, you can buy, sell, and trade any of these items with anyone in the world. OpenSea is currently the largest general marketplace for user-owned digital goods, with the broadest set of categories (200 and growing), the most items (over 4 million), and the best prices for new categories of items.

OpenSea is also a decentralized marketplace. Trading on on OpenSea happens through a smart contract, meaning that no central authority ever holds custody of your items. Instead, users store items in their wallet of choice - whether that's a mobile wallet like Coinbase Walletor Opera Touch or an in-browser chrome extension like MetaMask.

OpenSea lets you buy and sell crypto collectibles, gaming items, digital art, and other blockchain-based digital items. We have over 700 different projects on our platform, including trading card games like Gods Unchained and CryptoSpells, to collectible games like Axie Infinity and CryptoKitties, to digital art projects like SuperRare and Makersplace, to name systems like ENS (Ethereum Name Service).

Additionally, OpenSea is often useful for browsing the many types of digital collectibles. We offer a powerful searching and sorting mechanisms that lets you easily find the items you're looking for.

Description taken from https://opensea.io/faq