Personal POP3 in Gmail refers to the use of the POP3 protocol to retrieve emails from a Gmail account to a specific device. POP3 stands for Post Office Protocol, and it allows users to download emails onto their computer and remove them from the mail server. When accessing emails using the POP3 protocol, a copy of the emails is created and stored locally on the device. The originals are usually, but not always, removed from the mail server. This means that emails are tied to the specific device, and once an email is downloaded onto one device (and removed from the mail server), it cannot be accessed by another email client or device. Personal POP3 is great for users who only use one email client to access their emails.

In summary, personal POP3 in Gmail refers to the use of the POP3 protocol to download and store emails from a Gmail account to a specific device.