FYI stands for "for your information." It is a polite way to share a fact without demanding action. "FYI, the meeting moved to 3 PM." It is common in emails, memos, and text messages. It is neutral in tone. It does not accuse. It does not request. It just informs.

The acronym has been used since the 1940s. It appeared in military and government memos. It moved to business and then to everyday life. It is one of the few acronyms that works in professional settings. It is not too casual. It is not too formal. It is just right.

Related acronyms

• BTW: by the way, more casual.
• NRN: no reply necessary.
• FYSA: for your situational awareness, military.
• PSA: public service announcement, broader.

FYI can be passive-aggressive. "FYI, you left the dishes." The "for your information" softens the complaint. It makes it sound like a helpful note. The reader knows it is a reminder. The acronym is a tool. It can be used to inform or to nag. Tone is everything.