What is the difference between IMAP and POP3

 IMAP and POP3 are incoming email protocols which is used for downloading mails from mail server. you can use pop and IMAP with different email client like Microsoft Outlook, Mozilla Thunderbird etc.

Difference between IMAP and POP

IMAP (Internet Messaging Access protocol) email are stored on the server so Messages can be synced and accessed across multiple devices.
POP (post office protocol) download and store message on a single device. so emails can only be accessed from single device.

Which protocol to be used

If you are going to configure email account  on multiple device and you have guarantee internet access all time then IMAP would be good choice,

and if want to configure for single device and some time don't have internet connection then pop3 would be great choice.