bitcoind, the official reference Bitcoin full node software, is not really designed for high-traffic business use (such as high-volume storefronts). bcoin is an alternative Bitcoin full node, specifically designed for merchant/business use. It is software you download and install just like the official Bitcoin client, and once set up it offers an RPC API interface just like bitcoind does, but it comes with additional features business users would find useful.
For example: If you have ever tried to use the official bitcoind to set up, for example, a custom merchant storefront, you'd notice that a lot of what seems like common functionality is either missing or clunky. For example, it's missing the ability to check for transactions for a hierarchical key, aka xpub; with the bitcoind rpc you would have to individually subscribe to addresses. And due to the lack of xpubs, consider that to offer a customer a Bitcoin address to pay to, the way to create a Bitcoin address through the bitcoind RPC API necessarily requires that the private key be stored on the server, which is discouraged for public-facing servers.
If you use bitcoind for your storefront, you would need additional software/code libraries that include features like xpubs -- certainly will involve more parts to maintain, may be messy, will certainly be an inefficient design, and will probably run into design limits. So many storefronts will choose to use software like bcoin instead, to avoid those problems.
