IMAP stands for Internet Message Access Protocol, which is a standard email retrieval protocol. It allows users to access their email messages from multiple devices, such as a phone, laptop, and tablet, and organize messages into folders, flag messages for urgency or follow-up, and save draft messages on the server. Unlike POP (Post Office Protocol), which downloads and deletes messages from the server, IMAP stores email messages on a mail server and enables the recipient to view and manipulate them as though they were stored locally on their device(s).

IMAP works based on different types of requests, known as IMAP commands, which are similar to requests in HTTP. An IMAP command generally tells the server to do something or asks the server for some information. An IMAP server uses two ports: port 143 and port 993. Port 143 is used by email clients to connect through IMAP, while port 993 is used for secure connections over TLS/SSL encryption for emails.

In summary, IMAP is a protocol for receiving emails that allows users to access their email messages from multiple devices and organize them into folders on the server. It is different from POP in that it stores email messages on a mail server and enables the recipient to view and manipulate them as though they were stored locally on their device(s).