Extended public keys also known as xpub keys are a security feature of HD wallets (Hierarchical Deterministic). HD wallets extend a parent public key to derive child public keys. Extended public keys can generate “receive addresses” any time, without knowing the private keys. This is especially useful for a web store that has a lot of traffic. A merchant only needs to install their extended public key on their web server. The website doesn’t contain any private key but can produce unique addresses for each purchase. Despite its name extended public addresses should not be shared. They are only used for generating addresses. If your extended public key is made public all your previous and future transactions will be visible.