POP, or "Post Office Protocol," is a standard email protocol used to retrieve emails from a remote server. It allows users to download their emails to a local device, such as a computer or smartphone, making it easier to read and manage messages offline. The most common version is POP3, which supports multiple email clients and is widely used for personal email accounts. When using POP, emails are typically removed from the server after being downloaded, which can help free up server space. However, this means that emails are not accessible from other devices unless configured to leave copies on the server. This makes IMAP a popular alternative for users who want to access their emails from multiple devices.