IMAP stands for Internet Message Access Protocol, and it is a protocol that allows you to download messages from a mail providers servers, such as those for Gmail, onto your computer so you can use email clients like Microsoft Outlook, Apple Mail, or Mozilla Thunderbird to view and edit your email, even when you arent connected to the internet. With IMAP, email messages and attachments stay on the mail server even after you open them on your device, so you can get them from any of your devices at any time. In contrast, with POP, email messages and attachments are removed from the mail server after you get them on your device, so you cant get them from any other device. To sync your Gmail account using an IMAP email client, you need to enable IMAP for your Gmail account.