FYI is a common abbreviation of for your information (or interest, in some interpretations). It is especially common in American English

American English

American English is a set of dialects of the English language used mostly in the United States. Approximately two-thirds of the world's native speakers of English live in the United States....

.

It was originally used in The Twilight Zone

The Twilight Zone

The Twilight Zone is an American television anthology series created by Rod Serling. Each episode is a mixture of self-contained drama, psychological thriller, fantasy, science fiction, suspense, or horror, often concluding with a macabre or unexpected twist...

episode 002, "One for the Angels", aired on October 9, 1959; a pitchman (played by Ed Wynn) used it in a conversations with Death

Death (personification)

The concept of death as a sentient entity has existed in many societies since the beginning of history. In English, Death is often given the name Grim Reaper and, from the 15th century onwards, came to be shown as a skeletal figure carrying a large scythe and clothed in a black cloak with a hood...

.

"FYI" is commonly used in e-mail, instant messaging or memo messages, typically in the message subject, to flag the message as an informational message, with the intent to communicate to the receiver that he/she may be interested in the topic, but is not required to perform any action. It is also often used in informal and business spoken conversations, sometimes sarcastically.

Among Internet Standard

Internet standard

In computer network engineering, an Internet Standard is a normative specification of a technology or methodology applicable to the Internet. Internet Standards are created and published by the Internet Engineering Task Force .-Overview:...

s, FYIs are a subset of the Request for Comments

Request for Comments

In computer network engineering, a Request for Comments is a memorandum published by the Internet Engineering Task Force describing methods, behaviors, research, or innovations applicable to the working of the Internet and Internet-connected systems.Through the Internet Society, engineers and...

 (RFC) series.

The following description is taken from FYI 1, the FYI on FYIs:

The FYI series of notes is designed to provide Internet users with a central repository of information about any topics which relate to the Internet. FYIs topics may range from historical memos on "Why it was done this way" to answers to commonly asked operational questions.

See also

• FAQ
  FAQ
  Frequently asked questions are listed questions and answers, all supposed to be commonly asked in some context, and pertaining to a particular topic. "FAQ" is usually pronounced as an initialism rather than an acronym, but an acronym form does exist. Since the acronym FAQ originated in textual...
  
  
• FYG
  Fyg
  FYG is a common abbreviation of For Your Guidance.*FYG is commonly used in e-mail or memo messages, typically as the first thing on the subject line, to flag the message as an informational message that does not require a response....
  
  
• Internet slang
  Internet slang
  Internet slang is a type of slang that Internet users have popularized, and in many cases, have coined. Such terms often originate with the purpose of saving keystrokes. Many people use the same abbreviations in texting and instant messaging, and social networking websites...
  
  
• Military slang
  Military slang
  Military slang is an array of colloquial terminology used commonly by military personnel, including slang which is unique to or originates with the armed forces. It often takes the form of abbreviations/acronyms or derivations of the NATO Phonetic Alphabet, or otherwise incorporates aspects of...