What are IMAP and POP?
IMAP, the Internet message access protocol and POP, the Post Office Protocol, are the two most popular Internet standards protocols for sending and receiving email. Almost every modern email interface and most mail servers support both IMAP and POP as a means of transferring email messages over the Internet. Simply put, IMAP and POP enable you to download email from Google servers to your computer. This Google article explains these two Internet standards protocols in a little more detail.
What is an email client?
An email client, email reader, or mail user agent (MUA) is the software used to access and manage emails. There are many email clients available for different operating systems. Some of the more popular email clients are Microsoft Outlook, Mozilla Thunderbird, and Opera Mail. IMAP and POP support different email clients. Depending on which email client you'd like to use, you will have to configure your CloudMail account using either IMAP or POP. Luckily, Google has created these excellent articles to help learn more: