FIR or fir may refer to:

• Fir, a type of conifer tree
• USCGC Fir, either of two buoy tenders of the United States Coast Guard
• Fir (mathematics), free ideal ring (a mathematical concept)

Falling in Reverse is an American post hardcore band from Las Vegas, Nevada, formed in 2008, signed to Epitaph Records. The band is led by lead singer Ronnie Radke along with lead guitarist Christian Thompson, rhythm guitarist Derek Jones, bassist Zakk Sandler and drummer Ryan Seaman. They released their debut album, The Drug In Me Is You, on July 26, 2011, which peaked at number 19 on the Billboard 200, selling 18,000 copies in its first week of sales. "Raised by Wolves", "The Drug in Me Is You", "I'm Not a Vampire", "Good Girls Bad Guys" and "Pick Up the Phone" were all released as singles to promote the album. Their second studio album, Fashionably Late, was released on June 18, 2013, which peaked at number 17 on the Billboard 200. "Alone", "Fashionably Late", "Born to Lead", and "Bad Girls Club" were released as singles to promote the album. The band released three singles, "God, If You Are Above..." , "Guillotine IV (The Final Chapter)", and "Sexy Drug", in promotion of their third album Just Like You, which was released on February 24, 2015. However, on February 17, the full album stream was uploaded to fallinginreverse.com.

Firs (Abies) are a genus of 48–56 species of evergreen coniferous trees in the family Pinaceae. They are found through much of North and Central America, Europe, Asia, and North Africa, occurring in mountains over most of the range. Firs are most closely related to the genus Cedrus (cedar). Douglas firs are not true firs, being of the genus Pseudotsuga.